Basically to start I feel it’s easier to pre-paid for credits (just lightning sats). But I would need a way to deduct from the total paid for a specific pubkey.. as a pubkey is effectively the payer.

For example:

I pre-pay 5000 sats (linked to my pubkey)

I then pay 10/sat to publish my event to a relay - which is not an invoice, just a draw down from that pubkeys 5000 - so they now have 4990 sats pre-paid credits.

Account keeping should be virtual and not full wallets or anything complex.