I agree about the subscription fatigue. If there was a place to paste a renewable NWC connection string would you use it for a relay? I see coinos can support this.. I may attempt to implement this in the future, though it still depends on the friction of the users having to sign into, or paste their pubkey into my client to manage their subscription, they're viewing from another client and have no interest in that nor are even shown the landing page or etc. What is the problem you're having? Is the payment not working?

albyhub has zap planner, which lets you schedule lightning payments using an NWC string to lightning addresses at specific intervals. It also ha a field to put the recipient so I suppose one could put their npub, then the receiver would know the sub is paid. this is not client integrated which would be ideal, but seems like a tool client and relay devs could utilize for the function.