You could have a look at the app environment logs.
These can be found on you app project page on home.mendix.com
Choose 'Environments' menu item in the left menu panel.
Hi Ritka,
Are you publishing your app to the sandbox environment? If so, you can connect the debugger from your modeler to the sandbox environment to see where exactly the error is being thrown.
Here is some documentation on using the debugger remotely.
https://docs.mendix.com/howto/monitoring-troubleshooting/debug-microflows-remotely
I would also make sure you are testing exactly the same way as when you run the app locally. Is it possible that your microflow is dependent on a certain data that is not setup in your sandbox environment but is locally?