I take it that you correctly entered the required information for setting up the plugin? i.e. you had a successful connection when entering database name, username, password, and port?
If so, then I recommend you next step might be opening a support ticket with Dynatrace support: https://www.dynatrace.com/support/contact-support/
They will have more access to the necessary mechanisms to troubleshoot your issue.
Did you manage to fix the issue with the measurements returning null in the PostgreSQL Monitor?
One of my customers is experiencing the same
issue, they have provided admin rights to the user but still getting
null in all measurements.
As the plugin is a Community Plugin and not supported, I don't think
opening a support ticket with Dynatrace support might help.
What could we try?
Thanks a lot in advance!