Why is my Rental Professional app payment not processing?

[Mksk]

Hello,

The Rental Professional application allows you to include a calendar when purchasing a product which is then a service with a time slot. 

But when the user tries to pay (third party payment method with stripe) he gets "Your payment could not be processed yet, please try again in a few minutes" while it works fine for a regular purchase.

Anyone know where it could come from? Is it possible that shopify includes malicious apps ? (I'm newbe sorry for this question)

Thanks a lot for any help