I have purchased a AirPords Max with 6 months free at Apple Music was not able to redeem

Hi, I had that same issue with my Christmas gift. I’ve read tons of unhelpful solutions until I contacted apple directly via text message. I was told that the offer isn’t applicable to Apple ID’s that have had a previous subscription to Apple Music, including free trials. Hope this helped 🙁

Please contact Apple Support directly. They will help you with this issue: Get Support.

I ran into the exact same thing even after updating to latest iOS, but once I restarted my iPhone lol was good and the 6months free showed up and is now working for me. In case this helps someone.