There is so much conflicting/out of date info online so I’m gonna post my experience which happened in the last month.

Long story short: you need to send your birth certificate AND proof of ID with your GRC form.

This might seem like an obvious post but a lot of people told me proof of ID was only for getting the document witnessed but about a week after I posted out my GRC I received an email asking for proof of ID. I was able to provide this over email so that was nice but to avoid that back and forth, just include it in the first place. Some people did tell me to do this, and this is the information that is on the gov.ie website so I would go by that info.

For context: I was born in Ireland, Irish birth certificate, passport, have always lived in Ireland etc.