> ## 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). Bolta removes invisible characters from the request text but keeps tabs, line feeds, and carriage returns. Bolta rejects supplementary characters above U+FFFF, such as emoji, with `400`. See [Unsupported characters](/en/api-introduction/issuance-guide#unsupported-characters). ## 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 Issuance description: > Issue and amend e-tax invoices. [Calculating the issuance amount](/en/api-introduction/issuance-guide) | [Amendment types](/en/api-introduction/amendment-guide) - name: Tax Invoice Retrieval description: Retrieve e-tax invoice results and request processing status. - 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) | [Cash receipt webhooks](/en/api-introduction/webhook-cash-receipt) - name: Issuer description: > Register and manage businesses that act as tax invoice issuers. Certificate requirements depend on the issuance type. [Glossary](/en/api-introduction/glossary) | [Delegated issuance](/en/api-introduction/usecase-delegated) | [Brokered Tax Invoice Issuance](/en/api-introduction/usecase-brokered) - name: Certificate description: > Register and manage issuer certificates. [Certificate registration](/en/api-introduction/certificate-registration) paths: /v1/taxInvoices/{issuanceKey}/amend/changeSupplyCost: post: tags: - Tax Invoice Issuance 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). Bolta removes invisible characters from the request text but keeps tabs, line feeds, and carriage returns. Bolta rejects supplementary characters above U+FFFF, such as emoji, with `400`. See [Unsupported characters](/en/api-introduction/issuance-guide#unsupported-characters). parameters: - name: issuanceKey in: path description: Issuance request identifier required: true 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 allOf: - $ref: '#/components/schemas/TaxInvoiceItemsByTaxTypeConstraint' examples: Taxable: x-parity-id: 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 Zero-rate: x-parity-id: 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 or omitted. enum: - TAXABLE - ZERO_RATE - TAX_FREE examples: - TAXABLE - ZERO_RATE - TAX_FREE TaxInvoiceItemsByTaxTypeConstraint: type: object allOf: - if: properties: taxType: const: TAXABLE then: additionalProperties: true properties: items: items: additionalProperties: true properties: tax: type: integer required: - tax - if: properties: taxType: const: ZERO_RATE then: additionalProperties: true properties: items: items: additionalProperties: true properties: tax: const: 0 required: - tax - if: properties: taxType: const: TAX_FREE then: additionalProperties: true properties: items: items: additionalProperties: true properties: tax: type: 'null' 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 traceId: type: string description: Request trace identifier required: - code - message - traceId 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. ````