Apple Watch 5

I have an Apple Watch 5 and I have removed it completely from my iCloud! The iCloud lock is removed! I was going to give it to my sister however when pairing to her IPhone it will pair, ask which arm and I will have to agree to the agreement! After I agree to it it tries to go on then it gives me a message that the Apple Watch has a problem! I just removed it from my iPhone and I have never had a problem with it! I have a a Apple 6 on my phone now! I tried to pair the Apple 5 to my phone just to see if it would pair back to it and now it is giving me the message the Apple 5 has a problem! I am at loss as what else to do! I know the watch is fine!