Denial in question

I sent out a claim that had 20550 (LT) and 20600 (LT). the insurance paid 20600 but not the 20550 saying it was incidental to primary. I'm filing for appeal but i was wondering if anyone has seen this happen before and know how to prevent the denial from occurring again. maybe a modifier?

NCCI Edits

There's an edit with 20550 and 20600, because 20550 is bundled with 20600 usually. If it was a completely separate thing both can be paid, assuming there's enough documentation to support that they were different procedures, and that 20550 wasn't part of 20600. Since they're both on the same side the laterality modifier won't do it for you, but maybe 51 or 59 depending on which, if either, is appropriate.