RE: Debugging errors on CRM Dynamics online
Since the error is kind of BP error, it's more like raised from a sync plugin or workflow.
1. If it's a custom plug, you can enable plugin trace by going to system settings -> customization and enable plugin trace for all or exception.
Then you will get more iinformation from the plugin trace log by settings-> plugin trace log.
2. Or you switch to classic web client by applying the parameter https://....dynamics.com/main.aspx?forceclassic=1, during this period web client and UCI will exist side by side for a period.
3. Or you can raise an support to Microsoft to get the exception details by providing the activity ID.