redirect_uri error Paypal api

I'm trying to integrate paypal in my app but nothing is working. So now I'm just trying to query the api but I get errors too. Firstly, paypal provies an interactive tool to test their api. On step 2 you get a link. That's not working on my side.. The popup opens and I get :

Relying Party Validation error: redirect_uri provided in the request does
not match with the registered redirect_uri. Please check the request.

and that request is provided by paypal with theyr clientID and secret... I get the same error if I try with mine.

I tried to clean my cache. My redirect_uri is set in my app on paypal website, I'm in sandbox mode and login on the app is enabled

Any idea?