What I did so far: I installed the plugin, created and activated a Stripe account and entered all four keys and both client IDs in the plugin page. I also created a product with 3 different pricing plans in Stripe.
Hi @nicola.kegel When creating the Product and the Pricing Plans in Stripe, did you also create them as test data within Stripe? (You can toggle between your Stripe live and test data by using the small toggle on the left side of the Stripe dashboard).
If so, I would make sure that the test and live Pricing Plans have the same IDs. @keith’s post below has really helpful information on how to set this up