The error and cause of the 403 error is the following:
The 403 (Forbidden) HTTP Status code indicates that this project does not have permission to access the requested resource. This can happen if you are trying to invoke API request for a resource that is not part of your project e.g. if you have created a project with Visa Direct Product but are trying to use the same credentials to access Visa Consumer Transaction Controls.
Check for the following:
You are using a project and the credential for the project which includes the API being accessed.
Create a project and receive sandbox credentials for the API’s being called.
Add the API being called (if not already included) to the project with credentials that are being used.