I was going to post basically the same thing as
@RangerBob. It is a bit messy. Refilling an established prescription for your established patient in another state is not really a problem. Theoretically, you should send the prescription to the local CVS, then have them transfer it to another store. But no one is going to get into problems just refilling someone's HTN/diabetes/eye meds while they are on vacation. Controlled substances - that's a different ballgame.
Where it gets murky is addressing acute new issues for an established patient while someone is in a different state. That's definitely "not OK" legally. Although chance of getting into trouble is slim.
New prescription for someone you don't have an established relationship with - always a bad idea, whether you have an in state license or not. And if you do this, you MUST keep medical records of it, and follow all of the laws required of medical records and privacy / retention.
Perhaps of interest, I have wondered whether the USPS can generate additional revenue by opening telehealth stations. It's illegal to do a telehealth visit with your patient if they are in a state you don't have a license. But, if they are standing in a US post office and on their phone, that's federal property. You can have ANY state license and be legally practicing medicine. The USPS could set up some private rooms with a computer/camera/microphone and internet access, and charge for use for anyone wanting a telehealh visit.