2. Add the relevant certificate. Gmail requires you to add "Equifax root certificate" in order to connect successfully. Certificate has to be added to a Trust Store either at your application server level or Pega application level.
As you are using Pega 7.2.1 there should be more content below what you are showing in the screenshot, in collapsed areas with titles such as "Response data," "Errors and Exceptions," and "Debugging Information."
The details in there could be very useful in determining your issue.