I invited a friend via my referral code. They signed up on Kumos (https://kumos.subeta.net/register) and when they clicked the verification code in their email they got this error. I have wanted to invite other people as well but wondering if this is an unusual error (I've seen it twice now at least but no real reason or solution) or if I can help friends avoid the struggle. It apparently is and endless cycle of can't go anywhere until you verify but also can't verify.

Appreciate you both