Dear Daniele,
Thank you for using our plugin for VirtueMart. I am glad that you could create an account and support ticket directly on this site, it helps getting more efficient!
For your issue, it seems that you just need to copy and paste the Stripe API Keys. it will NOT "automatically takes it" from here, otherwise it would a serious security issue.
You should get your API keys for TEST here
https://dashboard.stripe.com/test/apikeys
See screenshot attached
and also your LIVE keys (once you are ready to go live)
https://dashboard.stripe.com/apikeys
Then copy the API keys into the VirtueMart plugin settings, Secret and Publishable. Be careful, they are in reverse order on Stripe.com.
Please let me know how it goes!
Kind regards,
Hervé