Prosite sandbox setting does not connect to paypal automaticaly


When I use my api credentials from Paypal with Prosites with a sanbox account, the link button to paypal payment does not work.

On a live environnement it work fine, but not on test mode. Is it important that test mode should work?

Also, when I try to update my account as a user, I click on your account and it direct me to the main multisite site and ask me to log in as the user on the main site, is it normal?

Many thanks