This goes for any medical expense, but also beware of the "Coordination of Benefits (COB) Questionnaire" required by your insurance company. They want to confirm your other coverage (e.g. Medicare) once a year, and sometimes the only way you know they are expecting it is when you get a call from your doctor's office that your claims are being silently denied. The insurance company won't send you an email, a call, or a ding in the portal, the language is buried at the bottom of a page of one of those PDFs you have to explicitly download.

I've had luck with just calling once a week or sending nastygrams asking why my claims are still denied, they usually say "oh that didn't go through I'll manually process that" and approve a few more each time. Incompetence vs maliciousness etc.