Hi
You can connect the debugger to any environment by selecting the connect option in studio pro and selecting the second option
You need to provide the app URL/debugger at the end of it and there must be a stored password as well from when you deployed the app on cloud.
If mendix cloud you can find this info in debugger info on sprintr
Alternatively, you can also access app logs to check the access error
Take a look at the documentation on remote debugging. It covers various hosting environments so hopefully the one you are using is covered there.
https://docs.mendix.com/refguide/debug-microflows-remotely/
For more information on using the debugger itself, have a look at his page.
https://docs.mendix.com/refguide/debug-microflows-and-nanoflows/
Good luck!