Ipad activation lock removal request shows "Session Expired Please enter a valid serial number / IMEI / MEID."

Hi, I forgot to sign out the apple account on ipad before I deleted my previous apple account. The account on the ipad can't be signed out now. I'd like to request to remove the activation lock for my ipad.

I input my email and ipad serial number with this link https://al-support.apple.com/#/al/request and then got a confirmation email. I click the link in the email but it shows "Session Expired Please enter a valid serial number / IMEI / MEID". And I'm sure that the serial number I input is correct. Wondering how to resolve this issue? Thanks!

[Edited by Moderator]