I’ve deployed your example and started a process instance.
After open the user task in the tasklist, I added a new variable with name xApproved, type Boolean and either check the box or not in the generic form. Hitting Complete, the process instances finished successfully.
Since I cannot update my original post, here a new description:
I have a user task Approve failed validation with a Boolean output parameter xApproved, which takes its value as ${approved}.
A conditional flow out of Approve failed validation uses the conditional string ${xApproved == true} .
I want to complete Approve failed validation with a generic form (i.e. used not only for Approve failed validation) that posts approved (not xApproved). So it is Approve failed validation concern to store approved in the individual variable xApproved.
But when I post approved with the generic form, I get the error message
Cannot submit task form c80503e9-3c55-11ea-886c-0242e97b0684: Unknown property used in expression: ${xApproved == true}. Cause: Cannot resolve identifier ‘xApproved’
Why can I not use xApproved in the conditional string of the conditional flow out of Approve failed validation?