Most API actions require an access token, which you must generate yourself once and store it safely. Access token must be supplied to VertexSMS API through HTTP headers. Header name: X-VertexSMS-Token you will see it in all examples.
Or as an alternative way you can pass the access token via query string at parameter.
Example:
EXAMPLEGET
GET https://api.vertexsms.com/someaction?at=eB52vNTPL9fO3rDrx8pYmVnj6nqceHNhnqceHNh
Generating token
You can generate access token via VertexSMS page, login to your account and then go to "MY ACCOUNT" ->"API"
Known limitations
Currently there are support only for one access token at the time, we are working for supporting multiple access tokens with different permissions and IP access blocking.