A 403 response from our token service (as-in when an integration attempts to obtain a single-use token from our gateway) will only be returned when there is a problem with the public API key used in that attempt, or there is a problem with the TID the public API key is tied to.
For example, a 403 response will be returned if the TID in use has been deactivated due to account termination.
Please verify the API key you are using is valid and that the account associated with the API is key active.