Natural or medicated mock cycle ERA after a chemical natural FET???

[Fingerscrossed38]

I had a natural fet and it resulted in early chemical.

My Dr wants to investigate why by doing an ERA but he's suggesting a medicated mock ERA cycle. Why world he do that when it was a natural fet? Surely results won't be accurate?? I've never done a natural cycle and I'm scared about messing with something that can work naturally. What would you do? Push for a natural ERA mock cycle or go with Dr?