Constraints Groovy Contract Validation

I have an error with constraints when i send the request, this is the error Debug message Exception while validating constraints, im doing the tutorial in the version 4.0 of the form i dont have problems, but when i duplicate to the 5.0 i have this error idk how to solve it

Hi,

I'm trying to make a complex data validation that requires to call a web service and also check if that result is in the database (Some kind of duplicate object validation). Is there any way to do that kind of validation in the Constraints of the Contract? Basically I need to add Groovy code as a constraint of the Contract. Is that posible? I'm using Bonita 7.5.1

Thanks in advance.