I believe I've made some progress with being able to receive the membership payments:

So in Studio > Stripe Connect all of my info appears to be correct and was in 'test' mode... 

BUT, in Studio > Payments > Settings I have an Organization page I made set as the 'Site Administrator'
I went to payment details within that organizations profile settings [yourdomain.una.io/page/payment-details] and I had only the live data entered into the Stripe section. I put that into 'Test' mode and entered the test API's, and it eliminated the error of "Your card was declined. Your request was in live mode, but used a known test card." I got the green check mark, it went through, then it hit the same error page "Cannot perform the action. Please report."

Not fixed, but it's progress. Going to continue troubleshooting.