[2021] Trying to purchase 16000 credits pack but an email "Potential fraud attempt notification" sent to mail

Hello,

I'm trying to buy 16000 rainbow credit packs via in-game steam purchases but a line "Something went wrong, please try again in few seconds" with an email titled above.
When I test to buy 600, 1200 credits pack and a steam overlay payment popup showed up normally but 16000 or the 7560 one got an error as I explained

How can I fix that? Thanks!