Just having the same issue now, can't redeem in game due to this error, can't send a ticket because it wants a serial code even though it says underneath the serial code box that you can just leave it blank if you don't have this info, i remember this happening to me a long time back, pretty crazy that they haven't fixed it yet.
Anyway i have no idea what the issue is but i will try what another said and do it on the home page (didn't know you could) and surprised Prime Gaming doesn't have that as a different method in the instructions like they do with other game instructions that have more than one option.
Edit: Code worked fine on the Home page.
Just having the same issue now, can't redeem in game due to this error, can't send a ticket because it wants a serial code even though it says underneath the serial code box that you can just leave it blank if you don't have this info, i remember this happening to me a long time back, pretty crazy that they haven't fixed it yet. Anyway i have no idea what the issue is but i will try what another said and do it on the home page (didn't know you could) and surprised Prime Gaming doesn't have that as a different method in the instructions like they do with other game instructions that have more than one option. Edit: Code worked fine on the Home page.