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The SimpleSell API follows REST conventions. Each resource, such as a parcel, has its own URL, and standard HTTP methods work on it: Actions that go beyond these methods, such as processing or cancelling a parcel, are POST requests to a sub-path of the resource, for example POST /parcels/{id}/process. The API uses HTTP status codes to indicate success or failure. See Error handling.

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Versioning

The API version is part of the base URL. The current version is v1. Within v1, we only make backward-compatible changes, such as new endpoints, new optional parameters, new response fields, or new values for fields like source. Make sure your integration ignores fields and values it doesn’t know. Breaking changes only come with a new version, such as v2. We announce new versions in advance and keep the previous version available for a transition period.

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Headers

The API always responds with JSON, except for document downloads. You don’t need to send an Accept header.

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Query parameters

Boolean query parameters, such as print or apply_products, only accept true or false. Other values, such as 1 or yes, return 400 Bad Request. List endpoints share conventions for sorting and filtering. See Pagination, sorting, and filtering.

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Request bodies

Requests that create or update resources take a JSON body. The reference of each endpoint, such as Create a parcel, lists the fields it accepts.
  • The API ignores fields it doesn’t know. Check the field names carefully, because a misspelled field is ignored without an error.
  • To remove the value of a field that can be empty, send null. The reference marks these fields as nullable.
When you update a resource with PATCH, the API only changes the top-level fields you send:
  • Fields you omit keep their current value.
  • Nested objects and arrays, such as receiver or items, are replaced as a whole. To change a single receiver field, send the complete receiver object.

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Responses

Responses wrap the requested data in a data object:
List endpoints return an array in data and pagination links in links. Document downloads return PDF files. Every response also contains an X-Request-ID header. Include it when you contact support about a request. See Contact support.

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Data formats

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Timestamps

The API only accepts timestamps in exactly this format: 2026-10-18T09:41:12Z. Timestamps with fractional seconds or a time zone offset, such as 2026-10-18T11:41:12+02:00, are rejected. Convert local times to UTC before you send them.

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Decimal values

Prices, weights, and dimensions are strings, not numbers. This avoids rounding errors with floating-point numbers. Use a dot as the decimal separator. Responses always contain the full number of decimal places. For example, if you send a weight of "1.2", the API returns "1.200".