@cicerone imposter,
Paid is used as an adjective...like a "paid" bill. Payed is past tense.If you say "I payed the bill yesterday", that would be correct.
Im sure over time both are acceptable, though. But if we want to nitpick, that's the CORRECT answer.
Now let's argue about "theater" vs. "theatre". I actually LOST a spelling bee in 3rd grade because i spelled it the "American" way. After they said I misspelled it, to which I replied, "yeah, in ENGLAND".