Contacts are optional — you can send to raw numbers — but storing them lets you send to a group instead of assembling a list on every request.

Endpoints

Create a contact

string
required
International format, e.g. 255766298542.
string
string
string

Groups

Group membership is managed separately:
You are responsible for having a lawful basis to message everyone on your lists, and for honouring opt-out requests. Uploading a purchased or scraped list breaches the acceptable use rules and can get your account suspended.