Cannot connect Vendor to stripe

Hi, I read and followed your guide about connect Split Stripe account. I created marketplace account on Stripe.com and I generated test key. When I try to connect a Vendor account on stripe everything is going well and when I finish the express registration and I goingig back to dashboard it looks like there is no conntection with stripe and I need to reconnect again to the express registration. It looks like nothing happens and I need to register again and again…
If I try to buy something from this store I got “Undefined” message during checkout.
Can you please help me?
maybe I’m missing something?

Thank you

Nick