> ## Documentation Index > Fetch the complete documentation index at: https://docs.bolta.io/llms.txt > Use this file to discover all available pages before exploring further. # Amend Tax Invoice - Change in Supply Cost > Pass, as items, how much has increased (+) or decreased (-) compared to the original. Provide each item's tax (`tax`) according to `taxType`. For detailed calculation examples, see the [Amendment types guide](/en/api-introduction/amendment-guide#change-in-supply-cost). ## OpenAPI ````yaml /openapi.en.yaml post /v1/taxInvoices/{issuanceKey}/amend/changeSupplyCost openapi: 3.1.0 info: title: Bolta API description: > The Bolta e-tax invoice API. [API Overview](/en/api-introduction/overview) | [Authentication guide](/en/api-introduction/authentication) | [Use cases](/en/api-introduction/usecase-b2b) version: 1.0.0 servers: - url: https://xapi.bolta.io description: Bolta API server security: - basicAuth: [] tags: - name: Tax Invoice description: > Issue and manage e-tax invoices. [Calculating the issuance amount](/en/api-introduction/issuance-guide) | [Amendment types](/en/api-introduction/amendment-guide) - name: Reverse Issuance description: > Request and manage reverse issuance of e-tax invoices. [Email-approval reverse issuance](/en/api-introduction/usecase-reverse-email) | [Simple-approval reverse issuance](/en/api-introduction/usecase-reverse-simple) - name: Cash Receipt description: > Issue, cancel, and check the status of cash receipts. Issuance and cancellation are asynchronous. Check the final result via webhook or the status API. [Cash receipt guide](/en/api-introduction/cash-receipt-guide) | [Webhook events](/en/api-introduction/webhook-events) - name: Supplier description: > Register and manage the supplier (issuer) that issues tax invoices. [Glossary](/en/api-introduction/glossary) | [Delegated issuance](/en/api-introduction/usecase-delegated) - name: Certificate description: > Register and manage the supplier's certificate. [Authentication guide](/en/api-introduction/authentication) paths: /v1/taxInvoices/{issuanceKey}/amend/changeSupplyCost: post: tags: - Tax Invoice summary: Amend Tax Invoice - Change in Supply Cost description: > Pass, as items, how much has increased (+) or decreased (-) compared to the original. Provide each item's tax (`tax`) according to `taxType`. For detailed calculation examples, see the [Amendment types guide](/en/api-introduction/amendment-guide#change-in-supply-cost). parameters: - name: issuanceKey in: path description: Issuance request identifier required: true schema: type: string - name: Supplier-Key in: header description: >- The identification key of the supplier (issuer). This is the key of the issuing party itself, not the supplied party (recipient). Use the supplierKey obtained from the Register Supplier API (POST /v1/suppliers); the supplied party information goes in the supplied field of the request body. It is managed independently per API key. [Glossary](/en/api-introduction/glossary) | [Authentication guide](/en/api-introduction/authentication) required: true example: SupplierKey_bf8paz schema: type: string requestBody: content: application/json: schema: type: object properties: date: $ref: '#/components/schemas/DateString' title: Write date description: Supply cost change date taxType: $ref: '#/components/schemas/TaxInvoiceTaxType' items: type: array minItems: 1 maxItems: 16 items: type: object properties: date: $ref: '#/components/schemas/DateString' title: Item supply date description: Item supply date name: type: string title: Item name description: Item name maxLength: 100 minLength: 1 unitPrice: type: - integer - 'null' title: Unit price description: Unit price minimum: 0 exclusiveMinimum: 0 examples: - 100 quantity: type: - integer - 'null' title: Quantity description: Quantity supplyCost: type: integer title: Supply cost description: Supply cost examples: - 1000 - -1000 tax: type: - integer - 'null' title: Tax description: Tax examples: - 0 - 100 - -100 specification: type: - string - 'null' title: Specification description: Specification maxLength: 60 description: type: - string - 'null' title: Item note description: Item note maxLength: 100 required: - date - name - supplyCost required: - date - taxType - items examples: taxable: summary: Taxable "Change in Supply Cost" amendment value: date: '2026-05-27' taxType: TAXABLE items: - date: '2026-05-27' name: Price adjustment unitPrice: null quantity: null supplyCost: -200000 tax: -20000 specification: null description: null zeroRate: summary: Zero-rate "Change in Supply Cost" amendment value: date: '2026-05-27' taxType: ZERO_RATE items: - date: '2026-05-27' name: Zero-rate price adjustment unitPrice: null quantity: null supplyCost: -200000 tax: 0 specification: null description: null responses: '200': description: '' content: application/json: schema: type: object properties: issuanceKey: $ref: '#/components/schemas/IssuanceKey' description: The IssuanceKey of the amended tax invoice required: - issuanceKey headers: {} '400': description: Bad request content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' '500': description: Internal server error content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' deprecated: false components: schemas: DateString: type: string format: date examples: - '2024-08-24' TaxInvoiceTaxType: type: string title: Tax type description: >- TAXABLE: taxable (e-tax invoice), ZERO_RATE: zero-rate (e-tax invoice), TAX_FREE: tax-exempt (invoice). For TAXABLE the item tax cannot be null; for ZERO_RATE every item's tax must be 0; for TAX_FREE every item's tax must be null. enum: - TAXABLE - ZERO_RATE - TAX_FREE examples: - TAXABLE - ZERO_RATE - TAX_FREE IssuanceKey: type: string description: >- An identifier for the issuance request. Note that the format and length may change. examples: - 8D529FAD3EBAE050B79CE943CCC7CEDE ErrorResponse: type: object description: The error response returned when an API request fails properties: code: type: string description: Error type identifier message: type: string description: Error description required: - code - message securitySchemes: basicAuth: type: http scheme: basic description: >- Base64-encode your API key and pass it. Enter the API key as the username and leave the password empty. ````