# REST API — Authentication


Source: https://vertexsms.com/en/api/authentication

Most API actions require an access token. Generate it once and store it safely. Supply the token via the `X-VertexSMS-Token` HTTP header (used in all examples), or via the `at` query-string parameter:

```
GET https://api.vertexsms.com/someaction?at=eB52vNTPL9fO3rDrx8pYmVnj6nqceHNhnqceHNh
```

## Generating a token

Sign in to your VertexSMS account, then go to **MY ACCOUNT → API**.

## Known limitations

Currently only one access token at a time is supported per account. Support for multiple tokens with different permissions and IP access blocking is on the roadmap.