Within the "Rewards" app from Perka/Clover there is an option within the preferences that is called "Diagnostics. Enable troubleshooting features when you are working with Clover support". What features could that be?
I read that integrating Crashlytics is recommended, but I am just wondering if anything else (technically) can be done to best cope with errors on merchant side.
This is something we have been tackling recently. Crashlytics is definitely a great idea.
On top of this you have a few options... Consider something like; Storing some verbose logging in a static or maybe shared preferences (so it is retained if your app crashes), then have a button which will http post the data to a webservice which can stick it in a database or send it via e-mail that sort of thing.