Please select the edit option of your process model in MWS. you will get an check box for the execution enabled, please select that and save.
Note: if you are modifying your process model in designer then you have to build and upload it again, then only you will get your latest process model in MWS.
I edit the option for the process model, after that, I tried to select the option “Execution Enabled”, but this option is not working. I mean, this option is not working. (not able to select)