> ## Documentation Index > Fetch the complete documentation index at: https://docs.ionicfi.com/llms.txt > Use this file to discover all available pages before exploring further. # Update an invoice item > Updates the amount and description of a pending item. An item already drained onto an invoice cannot be updated. ## OpenAPI ````yaml /openapi/invoices.yaml post /invoice_items/{id} openapi: 3.0.3 info: title: Ionic Invoices API version: '2026-05-30' description: | Invoices and invoice items. An invoice item is a pending charge recorded against a customer. When an invoice is created for that customer, every pending item in the invoice currency is drained onto the new draft as a line. A draft can be edited freely; finalizing it assigns a gapless, per-merchant/mode sequential number (for example `INV-000001`), applies tax, freezes the lines, and opens the invoice. Drafts carry no number, so an abandoned draft never consumes one and the finalized sequence is always contiguous. All monetary amounts are integers in the currency's minor unit (for example cents for USD). Timestamps are Unix epoch seconds. Identifiers are opaque, prefixed strings: invoices are `inv_…`, invoice items `ii_…`, and invoice lines `il_…`. Authentication uses a merchant secret key as a bearer token. Read endpoints require the `invoices:read` permission; write endpoints require `invoices:write`. The mode of the key (test or live) scopes which invoices and invoice items it can see, mutate, and drain. Live invoice numbers use `INV-000001` style labels; test invoice numbers use `TEST-INV-000001`. Mutating endpoints accept an optional `Idempotency-Key` header. Errors are returned as `{ "error": { "code": "...", "message": "..." } }`. A malformed path identifier returns 400. Concurrent updates are retried automatically; if they still conflict, the API returns 409 and the request can be retried. servers: - url: '{baseUrl}/v1' variables: baseUrl: default: https://api.ionicfi.com description: API base URL for your environment. security: - secretKey: [] tags: - name: Invoices description: Create, finalize, and manage invoices. - name: Invoice Items description: Pending charges that drain onto a customer's next invoice. paths: /invoice_items/{id}: parameters: - $ref: '#/components/parameters/InvoiceItemId' post: tags: - Invoice Items summary: Update an invoice item description: >- Updates the amount and description of a pending item. An item already drained onto an invoice cannot be updated. operationId: invoices_items_update parameters: - $ref: '#/components/parameters/IdempotencyKey' requestBody: required: true content: application/json: schema: $ref: '#/components/schemas/UpdateInvoiceItemRequest' responses: '200': description: The updated invoice item. content: application/json: schema: $ref: '#/components/schemas/InvoiceItem' '400': $ref: '#/components/responses/BadRequest' '401': $ref: '#/components/responses/Unauthorized' '403': $ref: '#/components/responses/Forbidden' '404': $ref: '#/components/responses/InvoiceItemNotFound' '409': $ref: '#/components/responses/ItemNotPending' '429': $ref: '#/components/responses/RateLimited' '500': $ref: '#/components/responses/InternalError' security: - secretKey: - invoices:write components: parameters: InvoiceItemId: name: id in: path required: true description: The invoice item id (`ii_…`). schema: type: string IdempotencyKey: name: Idempotency-Key in: header required: false description: >- A unique key that makes retries safe: the same key with the same request body returns the original response instead of repeating the operation. schema: type: string maxLength: 255 schemas: UpdateInvoiceItemRequest: type: object required: - amount - description properties: amount: type: integer description: New total amount in minor units, in the item's existing currency. description: type: string InvoiceItem: type: object required: - amount - created_at - currency - customer - description - id - invoice - metadata - object - pending - quantity - unit_amount - updated_at properties: id: type: string object: type: string enum: - invoice_item customer: type: string description: type: string quantity: type: integer unit_amount: type: integer amount: type: integer description: Total amount in minor units. currency: type: string invoice: type: string nullable: true description: The invoice this item was drained onto, or null while pending. price: type: string nullable: true pending: type: boolean metadata: type: object additionalProperties: type: string created_at: type: integer description: Unix epoch seconds. updated_at: type: integer Error: type: object properties: error: type: object properties: code: type: string description: A stable, machine-readable error code. message: type: string responses: BadRequest: description: The request was malformed or failed validation. content: application/json: schema: $ref: '#/components/schemas/Error' example: error: code: INVALID_DATA message: invalid currency Unauthorized: description: Missing or invalid API key. content: application/json: schema: $ref: '#/components/schemas/Error' Forbidden: description: The key lacks the required permission, or the merchant is not active. content: application/json: schema: $ref: '#/components/schemas/Error' InvoiceItemNotFound: description: No invoice item with that id is visible to this key. content: application/json: schema: $ref: '#/components/schemas/Error' example: error: code: INVOICE_ITEM_NOT_FOUND message: invoice item not found ItemNotPending: description: The invoice item is already assigned to an invoice. content: application/json: schema: $ref: '#/components/schemas/Error' example: error: code: INVOICE_ITEM_NOT_PENDING message: invoice item is already assigned to an invoice RateLimited: description: Too many requests. Honour the `Retry-After` header before retrying. content: application/json: schema: $ref: '#/components/schemas/Error' InternalError: description: | The API could not return a successful response. For a mutating request, retrieve the resource before retrying because the operation may have completed. content: application/json: schema: $ref: '#/components/schemas/Error' securitySchemes: secretKey: type: http scheme: bearer description: 'A merchant secret key (`sk_…`) sent as `Authorization: Bearer `.' ````