> ## Documentation Index > Fetch the complete documentation index at: https://docs.lmrp.uk/llms.txt > Use this file to discover all available pages before exploring further. # Join a unit > **Permission:** `cad.unit.self`. Also needs an active staff profile. Needs a signed-in user; service credentials are refused with `USER_REQUIRED`. **Access:** Browser session only. Adds the caller to an on-duty unit's crew. Take `unitId` and `version` from the on-duty list. Units carry at most eight crew. Records `CREW_JOINED` and advances the unit's `version`. ## OpenAPI ````yaml /api-reference/openapi.json post /cad/me/unit/join openapi: 3.1.0 info: title: Argus API version: 0.1.0 summary: The HTTP API behind the Argus web application. description: >- Argus is the operations platform for the UK London Mayfair ER:LC community. This document describes the API its own web application uses. **This is an internal application API.** It is not a stable public API: paths, fields and behaviour can change with any release, there is no versioning, and browser requests are tied to the application's own origin. Scoped service credentials exist for the community's own integrations. All paths are relative to `/api` on the deployment's origin. Responses are JSON, never cacheable, and carry an `X-Request-Id` header. servers: - url: http://localhost:3000/api description: Local development - url: '{origin}/api' description: A deployment. `origin` is that deployment's `APP_URL`. variables: origin: default: https://argus.example.org description: The application's public origin, with no trailing slash. security: [] tags: - name: Authentication description: >- Discord sign-in, Roblox account linking, the current user, and temporary Developer Access. - name: CAD Incidents description: >- Control's incidents: creation, editing, closure, and dispatching units to them. - name: CAD Units description: Control's view of operational units and their crew. - name: CAD Calls description: Incoming calls and how they become, or join, incidents. - name: CAD Events description: The append-only operational history. - name: MDT description: >- Self-service for the people crewing a unit: booking on and off, joining a unit, and changing its status. - name: Civilians description: 'The civilian portal: a member''s own characters, licences and vehicles.' - name: PNC Lookup description: >- Searching people and vehicles, full records, record history and official vehicle status. - name: PNC Licences description: Official changes to driving licences. - name: PNC Records description: Official records attached to people. - name: PNC Warrants description: Warrants and their lifecycle. - name: PNC Markers description: Markers and BOLOs on people and vehicles. - name: Staff description: Staff profiles and role membership. - name: Shifts description: Staff shifts. - name: Sessions description: Operational roleplay sessions. - name: Moderation description: Warnings, kicks and bans, with their delivery state. - name: Audit description: The append-only audit log. - name: Administration description: Accounts, roles and service credentials. - name: ERLC x-displayName: ER:LC description: Live data from the ER:LC private server. paths: /cad/me/unit/join: post: tags: - MDT summary: Join a unit description: >- **Permission:** `cad.unit.self`. Also needs an active staff profile. Needs a signed-in user; service credentials are refused with `USER_REQUIRED`. **Access:** Browser session only. Adds the caller to an on-duty unit's crew. Take `unitId` and `version` from the on-duty list. Units carry at most eight crew. Records `CREW_JOINED` and advances the unit's `version`. operationId: joinUnit requestBody: required: true content: application/json: schema: $ref: '#/components/schemas/UnitMembershipInput' example: unitId: cmg5z2unt000al508unt00001 version: 1 responses: '200': description: Success. headers: X-Request-Id: $ref: '#/components/headers/RequestId' content: application/json: schema: type: object properties: data: $ref: '#/components/schemas/CadUnit' required: - data example: data: id: cmg5z2unt000al508unt00001 callsign: MO12 agencyCode: MET type: RESPONSE status: AVAILABLE incidentId: null version: 2 createdAt: '2026-10-06T19:30:00.000Z' updatedAt: '2026-10-06T19:42:10.000Z' crew: - id: cmg5z3crw000bl508crw00001 unitId: cmg5z2unt000al508unt00001 identifier: Olivia Officer userId: cmg5x1k2a0000l508a1b2c3d4 joinedAt: '2026-10-06T19:30:00.000Z' leftAt: null user: id: cmg5x1k2a0000l508a1b2c3d4 displayName: Olivia Officer discord: id: '254781093445672960' username: olivia.officer avatar: null roblox: id: '4821093375' username: OliviaOfficer staff: id: cmg5x1k2a0001l5089f8e7d6c active: true - id: cmg5z3crw000cl508crw00002 unitId: cmg5z2unt000al508unt00001 identifier: Ben Baker userId: cmg5x1k2a0002l508b7c8d9e0 joinedAt: '2026-10-06T19:42:10.000Z' leftAt: null user: id: cmg5x1k2a0002l508b7c8d9e0 displayName: Ben Baker discord: null roblox: null staff: id: cmg5x1k2a000ol508staff0002 active: true incident: null '400': description: >- `INVALID_INPUT`: a parameter or body field fails validation; `details` lists each problem. `INVALID_JSON`: the body is missing or is not valid JSON. headers: X-Request-Id: $ref: '#/components/headers/RequestId' content: application/json: schema: $ref: '#/components/schemas/Error' example: error: code: INVALID_INPUT message: Request validation failed. details: - path: - unitId message: Invalid input requestId: 3f1c9d5e-7a42-4f0b-9c1e-8b6d2a4e5f70 '401': $ref: '#/components/responses/Unauthenticated' '403': description: >- `FORBIDDEN`: the caller lacks `cad.unit.self`. `STAFF_REQUIRED`: the caller is not active staff. `USER_REQUIRED`: the caller is a service credential. `INVALID_ORIGIN`: a browser request whose `Origin` is not the application's own. `ACCOUNT_DISABLED`: the account is suspended or disabled. headers: X-Request-Id: $ref: '#/components/headers/RequestId' content: application/json: schema: $ref: '#/components/schemas/Error' example: error: code: FORBIDDEN message: 'Permission required: cad.unit.self.' requestId: 3f1c9d5e-7a42-4f0b-9c1e-8b6d2a4e5f70 '404': description: '`NOT_FOUND`: no such unit.' headers: X-Request-Id: $ref: '#/components/headers/RequestId' content: application/json: schema: $ref: '#/components/schemas/Error' example: error: code: NOT_FOUND message: CAD record not found. requestId: 3f1c9d5e-7a42-4f0b-9c1e-8b6d2a4e5f70 '409': description: >- `CAD_CONFLICT`: the `version` is stale, the unit is off duty or empty, it already has eight crew, its incident is closed, or the caller is already crewed on a unit. `CONFLICT`: a concurrent change won. headers: X-Request-Id: $ref: '#/components/headers/RequestId' content: application/json: schema: $ref: '#/components/schemas/Error' example: error: code: CAD_CONFLICT message: Unit changed. Refresh before saving. requestId: 3f1c9d5e-7a42-4f0b-9c1e-8b6d2a4e5f70 '429': $ref: '#/components/responses/RateLimited' default: $ref: '#/components/responses/UnexpectedError' security: - sessionCookie: [] components: schemas: UnitMembershipInput: type: object properties: unitId: $ref: '#/components/schemas/Id' version: type: integer minimum: 1 description: The `version` you last read. A mismatch returns 409. required: - unitId - version additionalProperties: false CadUnit: type: object properties: id: $ref: '#/components/schemas/Id' callsign: type: string agencyCode: type: string type: type: string enum: - RESPONSE - PATROL - TRAFFIC - FIRE - AMBULANCE - SUPERVISOR - SPECIALIST status: type: string enum: - AVAILABLE - ASSIGNED - EN_ROUTE - ON_SCENE - BUSY - UNAVAILABLE - OFF_DUTY incidentId: anyOf: - $ref: '#/components/schemas/Id' - type: 'null' version: type: integer description: >- Optimistic concurrency token. Send the latest value with every change. createdAt: type: string format: date-time updatedAt: type: string format: date-time crew: type: array items: $ref: '#/components/schemas/CadCrewMember' description: Active memberships only, oldest first. incident: anyOf: - $ref: '#/components/schemas/CadIncident' - type: 'null' description: The incident the unit is assigned to. required: - id - callsign - agencyCode - type - status - incidentId - version - createdAt - updatedAt - crew - incident Error: type: object properties: error: type: object properties: code: type: string description: Stable machine-readable code. message: type: string details: description: >- Present on some errors. Validation failures carry an array of `{path, message}`; ER:LC failures carry `{availability: "unavailable"}`. required: - code - message requestId: type: string format: uuid description: >- Also sent as the `X-Request-Id` header. Quote it when reporting a problem. required: - error - requestId Id: type: string minLength: 1 maxLength: 64 pattern: ^[a-zA-Z0-9_-]+$ description: Argus record identifier. CadCrewMember: type: object properties: id: $ref: '#/components/schemas/Id' unitId: $ref: '#/components/schemas/Id' identifier: type: string description: Display-name snapshot taken when the membership began. userId: anyOf: - $ref: '#/components/schemas/Id' - type: 'null' joinedAt: type: string format: date-time leftAt: type: - string - 'null' format: date-time description: Null while the membership is active. user: anyOf: - $ref: '#/components/schemas/CrewIdentity' - type: 'null' description: Null only for legacy free-text history. required: - id - unitId - identifier - userId - joinedAt - leftAt - user CadIncident: type: object properties: id: $ref: '#/components/schemas/Id' number: type: integer description: Sequential. Displayed as `CAD-000142`. status: type: string enum: - OPEN - CLOSED priority: type: string enum: - IMMEDIATE - URGENT - ROUTINE - LOW type: type: string location: type: string description: type: string controlNotes: type: string version: type: integer description: Optimistic concurrency token. createdAt: type: string format: date-time updatedAt: type: string format: date-time closedAt: type: - string - 'null' format: date-time required: - id - number - status - priority - type - location - description - controlNotes - version - createdAt - updatedAt - closedAt CrewIdentity: type: object properties: id: $ref: '#/components/schemas/Id' displayName: type: string discord: type: - object - 'null' properties: id: type: string username: type: string avatar: type: - string - 'null' required: - id - username - avatar roblox: type: - object - 'null' properties: id: $ref: '#/components/schemas/RobloxId' username: type: string required: - id - username staff: type: - object - 'null' properties: id: $ref: '#/components/schemas/Id' active: type: boolean required: - id - active required: - id - displayName - discord - roblox - staff RobloxId: type: string pattern: ^[1-9][0-9]{0,19}$ description: Roblox user ID, as a string. headers: RequestId: schema: type: string format: uuid description: Identifies this request in server logs. RetryAfter: schema: type: integer minimum: 1 description: Seconds to wait before trying again. responses: Unauthenticated: description: >- `UNAUTHENTICATED`: no session cookie, or an invalid, expired or revoked service credential. `SESSION_EXPIRED`: the session has ended. headers: X-Request-Id: $ref: '#/components/headers/RequestId' content: application/json: schema: $ref: '#/components/schemas/Error' example: error: code: UNAUTHENTICATED message: Sign in to continue. requestId: 3f1c9d5e-7a42-4f0b-9c1e-8b6d2a4e5f70 RateLimited: description: >- `RATE_LIMITED`: more than 180 reads or 60 writes in a minute for this caller. headers: X-Request-Id: $ref: '#/components/headers/RequestId' Retry-After: $ref: '#/components/headers/RetryAfter' content: application/json: schema: $ref: '#/components/schemas/Error' example: error: code: RATE_LIMITED message: Too many requests. requestId: 3f1c9d5e-7a42-4f0b-9c1e-8b6d2a4e5f70 UnexpectedError: description: >- Any other failure, in the same error envelope: `INTERNAL_ERROR` (500), `METHOD_NOT_ALLOWED` (405), `BODY_TOO_LARGE` (413, over 16 KiB) or `UNSUPPORTED_MEDIA_TYPE` (415, body not sent as `application/json`). headers: X-Request-Id: $ref: '#/components/headers/RequestId' content: application/json: schema: $ref: '#/components/schemas/Error' example: error: code: INTERNAL_ERROR message: The request could not be completed. requestId: 3f1c9d5e-7a42-4f0b-9c1e-8b6d2a4e5f70 securitySchemes: sessionCookie: type: apiKey in: cookie name: __Host-argus-session description: >- The opaque session cookie set by Discord sign-in. Named `argus-session` outside production. HttpOnly, so scripts cannot read it; same-origin requests send it automatically. Requests other than GET must also carry an `Origin` header equal to the application's own origin. ```` This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.