> ## Documentation Index
> Fetch the complete documentation index at: https://docs.superx.so/llms.txt
> Use this file to discover all available pages before exploring further.

# Add a contact list member

> Add a person to a list you created, by `handle` (live profile lookup)
or by `x_user_id` (numeric X user id already known to SuperX).
Exactly one of the two. Naturally idempotent: adding someone already
in the list returns 200 with the existing member and
`duplicate: true`, and writes nothing. Main account only; needs the
write scope. No `Idempotency-Key` support (none is needed).

Counts against a separate live-contact-enrichment rate limit (varies
by plan), in addition to the normal write limits.




## OpenAPI

````yaml /api-reference/openapi.yaml post /v1/contact-lists/{id}/members
openapi: 3.1.0
info:
  title: SuperX API
  version: 1.0.0
  description: >
    The SuperX public API: your Twitter/X content, analytics, audience and

    scheduling data over REST.


    All endpoints require an API key (`Authorization: Bearer sxk_...`) except

    `GET /v1/docs`. Keys are created in the SuperX app under Account > API / MCP
    / CLI

    and are server-side secrets.


    Timestamps are UTC ISO-8601 in both directions; inputs must carry an
    explicit

    `Z` or numeric offset. Every authenticated response carries

    `X-RateLimit-Limit`, `X-RateLimit-Remaining` and `X-RateLimit-Reset`
    headers.
  contact:
    name: SuperX
    url: https://superx.so
servers:
  - url: https://api.superx.so
security:
  - apiKey: []
tags:
  - name: Identity
  - name: Content
  - name: Analytics
  - name: Inspiration
  - name: Audience
  - name: Contact Lists
  - name: Signals
  - name: Media
  - name: Scheduling
  - name: Tags
  - name: Context
  - name: Queue
  - name: Articles
  - name: Meta
paths:
  /v1/contact-lists/{id}/members:
    post:
      tags:
        - Contact Lists
      summary: Add a contact list member
      description: |
        Add a person to a list you created, by `handle` (live profile lookup)
        or by `x_user_id` (numeric X user id already known to SuperX).
        Exactly one of the two. Naturally idempotent: adding someone already
        in the list returns 200 with the existing member and
        `duplicate: true`, and writes nothing. Main account only; needs the
        write scope. No `Idempotency-Key` support (none is needed).

        Counts against a separate live-contact-enrichment rate limit (varies
        by plan), in addition to the normal write limits.
      operationId: addContactListMember
      parameters:
        - name: id
          in: path
          required: true
          description: The list id from `GET /v1/contact-lists`.
          schema:
            type: string
        - $ref: '#/components/parameters/AccountId'
      requestBody:
        required: true
        content:
          application/json:
            schema:
              type: object
              properties:
                handle:
                  type: string
                  description: X username, with or without the @.
                x_user_id:
                  type: string
                  description: Numeric X user id.
            examples:
              byHandle:
                value:
                  handle: founderhandle
              byId:
                value:
                  x_user_id: '944883311'
      responses:
        '200':
          description: Already a member; nothing changed.
          content:
            application/json:
              schema:
                type: object
                properties:
                  data:
                    $ref: '#/components/schemas/AddedContactListMember'
                  duplicate:
                    type: boolean
              example:
                data:
                  id: m1a2b3c4d5e6f7g8h9i0j
                  x_user_id: '944883311'
                  username: founderhandle
                  name: Founder Name
                  avatar_url: https://pbs.twimg.com/profile_images/...
                  added_at: '2026-06-25T11:00:00.000Z'
                duplicate: true
        '201':
          description: The member was added.
          content:
            application/json:
              schema:
                type: object
                properties:
                  data:
                    $ref: '#/components/schemas/AddedContactListMember'
              example:
                data:
                  id: m1a2b3c4d5e6f7g8h9i0j
                  x_user_id: '944883311'
                  username: founderhandle
                  name: Founder Name
                  avatar_url: https://pbs.twimg.com/profile_images/...
                  added_at: '2026-07-08T10:00:00.000Z'
        '400':
          $ref: '#/components/responses/SystemListReadOnly'
        '401':
          $ref: '#/components/responses/Unauthorized'
        '403':
          $ref: '#/components/responses/WriteForbidden'
        '404':
          $ref: '#/components/responses/ListOrUserNotFound'
        '429':
          $ref: '#/components/responses/RateLimited'
        '502':
          $ref: '#/components/responses/UpstreamError'
        '503':
          $ref: '#/components/responses/UpstreamUnavailable'
components:
  parameters:
    AccountId:
      name: account_id
      in: query
      required: false
      description: >-
        Account to act on, from `GET /v1/accounts`. Defaults to your main
        account. An id outside your accounts returns `404 account_not_found`.
      schema:
        type: string
  schemas:
    AddedContactListMember:
      type: object
      description: Compact member shape returned by the add endpoint.
      properties:
        id:
          type: string
        x_user_id:
          type: string
        username:
          type: string
          nullable: true
        name:
          type: string
          nullable: true
        avatar_url:
          type: string
          nullable: true
        added_at:
          type: string
          format: date-time
          nullable: true
    ErrorEnvelope:
      type: object
      required:
        - error
      properties:
        error:
          type: object
          required:
            - code
            - message
          properties:
            code:
              type: string
              description: Stable machine-readable error code.
            message:
              type: string
            retry_after:
              type: integer
              description: Seconds to wait before retrying (rate-limit errors only).
    LegacyErrorEnvelope:
      type: object
      required:
        - error
      description: |
        Legacy shape used ONLY by the shared subscription middleware: a plain
        string `error` field. Seen on `403` when the subscription has lapsed
        (string starts with "subscription_required:") and on `500` when
        subscription verification fails (string starts with "internal_error:").
      properties:
        error:
          type: string
          example: >-
            subscription_required: The SuperX API requires an active
            subscription
  responses:
    SystemListReadOnly:
      description: >-
        Member add/remove on a system list (`system_list_read_only`), or a
        malformed body (`invalid_parameter`).
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/ErrorEnvelope'
          example:
            error:
              code: system_list_read_only
              message: System lists are managed automatically and can't be edited.
    Unauthorized:
      description: >-
        Missing/malformed Authorization header (`unauthorized`) or an
        unknown/revoked key (`invalid_api_key`).
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/ErrorEnvelope'
          example:
            error:
              code: invalid_api_key
              message: Unknown or revoked API key
    WriteForbidden:
      description: >-
        Read-only key (`insufficient_scope`), a linked or shared account
        (`writes_main_account_only`), or a lapsed subscription (legacy string
        envelope).
      content:
        application/json:
          schema:
            oneOf:
              - $ref: '#/components/schemas/ErrorEnvelope'
              - $ref: '#/components/schemas/LegacyErrorEnvelope'
          example:
            error:
              code: insufficient_scope
              message: >-
                This API key is read-only. Create a key with the write scope to
                use this endpoint.
    ListOrUserNotFound:
      description: >-
        The list id is not one of your lists (`list_not_found`), or the handle
        did not match an X account (`user_not_found`).
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/ErrorEnvelope'
          example:
            error:
              code: user_not_found
              message: No X account matches that handle.
    RateLimited:
      description: Rate limit exceeded (limits vary by plan). Honor Retry-After.
      headers:
        Retry-After:
          description: Seconds to wait before retrying.
          schema:
            type: integer
        X-RateLimit-Limit:
          $ref: '#/components/headers/X-RateLimit-Limit'
        X-RateLimit-Remaining:
          $ref: '#/components/headers/X-RateLimit-Remaining'
        X-RateLimit-Reset:
          $ref: '#/components/headers/X-RateLimit-Reset'
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/ErrorEnvelope'
          example:
            error:
              code: rate_limited
              message: >-
                Rate limit exceeded for the Pro plan (30 requests/min). Upgrade
                for higher limits.
              retry_after: 42
    UpstreamError:
      description: A dependent SuperX service returned an unexpected response.
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/ErrorEnvelope'
          example:
            error:
              code: upstream_error
              message: Failed to fetch scheduled posts. Try again shortly.
    UpstreamUnavailable:
      description: >-
        The scheduling service is temporarily unreachable. Safe to retry; reuse
        your Idempotency-Key on POST.
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/ErrorEnvelope'
          example:
            error:
              code: upstream_unavailable
              message: >-
                The scheduling service is temporarily unavailable. Retry with
                the same Idempotency-Key.
  headers:
    X-RateLimit-Limit:
      description: The limit of the rate window closest to exhaustion.
      schema:
        type: integer
    X-RateLimit-Remaining:
      description: Requests remaining in that window.
      schema:
        type: integer
    X-RateLimit-Reset:
      description: Unix timestamp (seconds) when that window resets.
      schema:
        type: integer
  securitySchemes:
    apiKey:
      type: http
      scheme: bearer
      description: >-
        A SuperX API key ("sxk_..."), created in the SuperX app under Account >
        API / MCP / CLI. Keys are server-side secrets.

````