Hi Joilson,
There is no possibility to add a blocking code(like server call) in the collection change event in diagram. We request you to share us more details about your requirement. We try to give the alternative solution.
Regards,
Gowtham
Hello, thanks for your answer, our business logic is similar to something like:
https://gist.github.com/jrabello/8e5809345f9322cdc6533112fd93da03