> ## Documentation Index > Fetch the complete documentation index at: https://www.finseed.es/docs/llms.txt > Use this file to discover all available pages before exploring further. # Retrieve a number series > Returns a single number series by id, in the same shape as each row of the list endpoint. The series must belong to the environment the API key belongs to, otherwise the response is a 404. ## OpenAPI ````yaml /api-reference/openapi.json get /v1/number_series/{id} openapi: 3.1.0 info: title: Finseed API version: 1.0.0 description: >- REST API for programmatic Verifactu invoicing. Every request is sent over HTTPS and authenticated with an API key passed as a bearer token. Each key is scoped to a single environment (test or live). Payloads are JSON with snake_case fields: amounts are integer minor units (cents) and timestamps are RFC 3339 in UTC. List endpoints are cursor-paginated. Errors return a small application/json envelope with a stable, machine-readable `code`. servers: - url: https://api.finseed.es security: - bearerAuth: [] paths: /v1/number_series/{id}: get: tags: - Number Series summary: Retrieve a number series description: >- Returns a single number series by id, in the same shape as each row of the list endpoint. The series must belong to the environment the API key belongs to, otherwise the response is a 404. operationId: getNumberSeries parameters: - name: id in: path required: true description: Opaque number series identifier — the `id` from a list row. schema: type: string responses: '200': description: The requested number series. content: application/json: schema: $ref: '#/components/schemas/NumberSeries' '401': description: >- Authentication failed: the API key is missing, malformed, or revoked. Send a valid key as a bearer token in the `Authorization` header. Each key is bound to a single environment (test or live). content: application/json: schema: $ref: '#/components/schemas/ErrorEnvelope' example: code: unauthorized detail: >- Authentication failed. Send your API key as a bearer token in the `Authorization` header. Keys are scoped to one environment, so a test key cannot read live data and vice versa. errors: [] doc_url: https://www.finseed.es/docs/api-reference/errors#unauthorized '404': description: >- No number series matches the supplied identifier in the environment the API key belongs to. A number series created with a live key is not visible to a test key, and vice versa. content: application/json: schema: $ref: '#/components/schemas/ErrorEnvelope' example: code: number_series_not_found detail: >- No number series matches that identifier in this environment. Note that test and live keys see different number series. errors: [] doc_url: >- https://www.finseed.es/docs/api-reference/errors#number_series_not_found '500': description: >- An unexpected error occurred on our side. No partial work is persisted, so the request can be retried safely. content: application/json: schema: $ref: '#/components/schemas/ErrorEnvelope' example: code: internal_error detail: >- Something went wrong on our side. The request did not complete and can be retried safely. errors: [] doc_url: >- https://www.finseed.es/docs/api-reference/errors#internal_error components: schemas: NumberSeries: type: object properties: id: type: string description: Opaque, prefixed number series identifier. example: ns_clx123abc456 prefix: type: string description: >- Prefix stamped on every invoice number of this series, stored normalized: whitespace removed and letters uppercased. example: F type: type: string description: >- What the series numbers: regular invoices (`standard`) or rectifying invoices (`rectifying`). This is an extensible enum: new values may be added in the future, so clients must tolerate values not listed here. Known values: standard, rectifying. example: standard first_value: type: integer description: The number assigned to the first invoice on this series. example: 1 next_value: type: integer description: The number the next invoice on this series will take. example: 42 number_digits: type: integer description: >- Zero-padding width of the numeric part of the invoice number. 0 means no padding. example: 5 is_default: type: boolean description: >- Whether this is the default series of the environment. Read-only: only the series seeded with the environment can be the default. example: false created_at: type: string description: Creation timestamp, RFC 3339 in UTC. example: '2026-06-01T09:30:00Z' required: - id - prefix - type - first_value - next_value - number_digits - is_default - created_at additionalProperties: false description: >- An invoice numbering series as exposed by the public API. Invoice numbers are always assigned by the server: prefix plus a gapless, zero-padded counter. A series is immutable once created. example: id: ns_clx123abc456 prefix: F type: standard first_value: 1 next_value: 42 number_digits: 5 is_default: false created_at: '2026-06-01T09:30:00Z' ErrorEnvelope: type: object properties: code: type: string description: >- Stable, machine-readable error code. The branch key. This is an extensible enum: new values may be added in the future, so clients must tolerate values not listed here. Known values: invalid_request, unauthorized, invoice_not_found, download_link_expired, number_series_not_found, number_series_prefix_taken, number_series_in_use, customer_not_found, customer_ambiguous, idempotency_conflict, rate_limited, invalid_number_series, invalid_tax_rate, invalid_tax_data, invalid_tax_id, tax_id_type_country_mismatch, insufficient_recipient_data, simplified_amount_exceeded, simplified_incompatible_tax_type, invalid_recargo_equivalencia, aeat_mandate_not_approved, no_active_subscription, tax_id_validation_unavailable, invalid_rectifies_reference, rectified_invoice_not_found, invoice_already_voided, invoice_already_replaced, invoice_not_family_tip, invoice_pending_at_aeat, invoice_not_rectifiable_at_aeat, family_balance_below_zero, replacement_total_negative, reason_incompatible_with_recipient, recipient_overrides_not_allowed_for_differences, rectifying_series_invalid, external_reference_invalid, external_reference_matches_existing_invoice, rectified_amounts_required_for_substitution, line_item_without_tax_items, internal_error. example: invalid_request detail: type: string description: Human-readable, context-specific explanation. example: The query parameters are not valid. errors: type: array items: type: object properties: field: type: string description: Location of the offending value (JSON path). example: limit code: type: string description: Machine-readable validation issue code. example: too_big message: type: string description: Human-readable explanation of the field-level issue. example: Number must be less than or equal to 100 required: - field - code - message additionalProperties: false description: >- Field-level issues. Always present; empty unless this is a validation failure. doc_url: type: string description: Link to the reference documentation for this error code. example: https://www.finseed.es/docs/api-reference/errors#invalid_request required: - code - detail - errors - doc_url additionalProperties: false description: >- Uniform error body returned for every non-2xx response (application/json). securitySchemes: bearerAuth: type: http scheme: bearer description: API key sent as a bearer token in the `Authorization` header. ````