The Numbers API enables you to search for, view, and activate numbers. It's considered a precursor to other APIs in the Sinch product family. The numbers API can be used in tandem with any of our APIs that perform messaging or calling. Once you have activated your numbers, you can then use the various other APIs, such as SMS or Voice, to assign and use those numbers.

Numbers REST formats and conventions

Let's take a brief look at some of the formats used in the REST API.


JSON (application/json) is the content type of both requests and responses if not otherwise specified.

Requests with invalid JSON will be rejected.

Null values

Null values can be omitted in requests and will be omitted in responses. In some cases, explicitly setting null will overwrite a previously set value with null.

Phone numbers

Only phone numbers in E.164 standard format are accepted by the API.


  • US phone number: +13059394139
  • UK phone number: +447478727259
  • SE phone number: +46113232516

Status codes

A summary of status codes can be found on the HTTP status codes page.

New features

New features might result in additional request and response parameters. New request parameters will either have a default value or be considered optional to retain backwards compatibility. It's highly recommended to ignore any unexpected parameters when reading JSON in API responses and in callback handlers.