Unable to enter-modify transactions (android app)

I bought personal finance premium app. Evererything runs ok except when I try to enter a new transaction or modify an existing one. The problem seems to be with the amount. When I validate the amount it always gets to 0. The only way I can create a transaction is from an existing one on the description but when I modify the amount it gets back to 0. My phone's android version is 8.0.0.

Thanks for your help

Miquel