Here is the information to get the API Token you need in order to use the WebService (API) and the SDKs. Remember that all the information related to the API and SDK is in http://payhub.github.io/slate/
In order to get the 3rd party API token you have to:
1- Login in the Virtual Terminal, go to Admin and Terminal/General
2- Check that your account has a 3rd Party API defined. If it is not defined you have to request the creation of a new one. If you have a 3rd Party API terminal defined you can continue.
3- Go back to admin screen and go to 3rd Party API option