you can use ‘ExecuteMicroflowasUser’ in community commons to call the microflow which completed the commercial approver user task
Refer the below forum link for the same error
Hope it helps!!!
The error seems to be something linked to permissions of users. I think the user with whom you are logged in when denying on the technical part does not have the permissions to make a decision in the commercial part because the task is not assigned to them. Perhaps you could check whether that is the case? Because if the assignee is not the user you are logged in with, you should not be able to change that. However you can normally write a microflow where you change the assignee to the user currently doing the change.
Let me know if this has helped