I'm getting the exact same error with the same stated reasons, none of which apply to me. Family plan, in the US, paid up to date with a recurring charge directly from Spotify, never redeemed an offer like this before.
I'm having the same issue and I'm utterly bewildered. I actually utilized Spotify's live chat function and was in contact with someone in customer service, but that person told me I needed to reach out to someone at the Google store (which makes no sense to me).
I'm having the same issue as well. I've read the T&C at least 3 times and can't understand why I'm getting the same message that you posted. I'm so frustrated because I don't want to miss out on the offer.