I was trapped. I already register and get fail before I read:
"Registration will begin shortly!
DO NOT REGISTER YET, TRANSACTION WILL FAIL !!!"

I think, you do not put airdrop link in your page, or disable any button before airdrop begin.
Correct, but people should read before submitting.
That's how scammers can scam people because they don't read

AIRDROP IN 20 MINUTES!!!!