Problem with incoerent local currency in contribution
Looks like the decimal delimiter present at civicrm/admin/setting/localization?reset=1 is configured as a comma (,) instead of a default ..

Civi might not be handling this correctly when the record payment form is loaded. The value of the total amount defaults to 1.0 instead of considering the delimiter configured for your site, i.e, 1,0. Either this might be a bug which needs to be fixed OR you can try using the default . in the above settings and check if it fixes for you.