All calls to the Phaxio API should be made to https://api.phaxio.com/v1. For most calls you will need to pass in your API key and API secret as parameters. You can find your API credentials on the "API Settings" page. In Phaxio, there are two types of credentials: live and test.
If you make an API call with a live key, your balance will decrease if you perform operations that cost money (e.g. you send a fax). However, if you make calls with test keys, the Phaxio system will simulate faxes being sent or received and your balance will not be affected.
All Phaxio API responses are formatted in JSON. Need an XML response? Too bad. JSON is awesome. Click here to learn more about it.
Parameters that look like this are optional, whereas all other parameters are required.