Does nexus have to be from an MD?

Asked my Dr to write me a nexus, he said he would. Went in for a visit to review all my evidence and what exactly what I wanted to nexus for. He agreed. His NP was also in the room who also agreed. Go to pick up the letter today and it’s signed by the NP. I have a really good relationship with my Dr and have been going to him for years so I don’t want to sound ungrateful. However, I also don’t want to submit, wait 6-9 months and get denied cuz of the nexus not being signed by an NP. I can’t really find anything anywhere.