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

# Topup Key

> Top up a key's prepaid balance via x402 USDC payment (#434).

The x402 middleware prices this path at {usd} dollars and verifies payment
before this handler runs; the amount paid is credited 1:1. Each priced call
is then debited at the price in the pricing table.



## OpenAPI

````yaml /api-reference/openapi.json post /v1/keys/topup/{usd}
openapi: 3.1.0
info:
  title: LimitGuard.ai
  description: Trust Intelligence API - Entity verification and risk scoring
  version: 0.1.0
servers:
  - url: https://api.limitguard.ai
security: []
paths:
  /v1/keys/topup/{usd}:
    post:
      summary: Topup Key
      description: >-
        Top up a key's prepaid balance via x402 USDC payment (#434).


        The x402 middleware prices this path at {usd} dollars and verifies
        payment

        before this handler runs; the amount paid is credited 1:1. Each priced
        call

        is then debited at the price in the pricing table.
      operationId: topup_key_v1_keys_topup__usd__post
      parameters:
        - name: usd
          in: path
          required: true
          schema:
            type: integer
            minimum: 5
            description: Whole US dollars to add to the prepaid balance
            title: Usd
          description: Whole US dollars to add to the prepaid balance
      responses:
        '200':
          description: Successful Response
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/KeyTopupResponse'
        '422':
          description: Validation Error
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/HTTPValidationError'
      security:
        - APIKeyHeader: []
components:
  schemas:
    KeyTopupResponse:
      properties:
        key_id:
          type: string
          title: Key Id
          description: Key identifier (SHA-256 hash prefix)
        tier:
          type: string
          title: Tier
          description: Tier label (unchanged by a top-up)
        credited_usd:
          type: number
          title: Credited Usd
          description: USD credited to the prepaid balance by this payment (1:1)
        balance_usd:
          type: number
          title: Balance Usd
          description: Prepaid balance after this credit
      type: object
      required:
        - key_id
        - tier
        - credited_usd
        - balance_usd
      title: KeyTopupResponse
      description: Response after topping up a key's prepaid balance via x402.
    HTTPValidationError:
      properties:
        detail:
          items:
            $ref: '#/components/schemas/ValidationError'
          type: array
          title: Detail
      type: object
      title: HTTPValidationError
    ValidationError:
      properties:
        loc:
          items:
            anyOf:
              - type: string
              - type: integer
          type: array
          title: Location
        msg:
          type: string
          title: Message
        type:
          type: string
          title: Error Type
      type: object
      required:
        - loc
        - msg
        - type
      title: ValidationError
  securitySchemes:
    APIKeyHeader:
      type: apiKey
      in: header
      name: X-API-Key

````