This was a problem with the form and nothing on your end, the form didn't recognise your SteamID as it is a digit shorter than most but the form has been fixed to recognise yours now and you can now post your appeal.
the steam ID you provided does match the one on the banned account. Could you provide a screenshot of the error you're seeing?
I will tag the staff member that issued the punishment as well. @Draxen
This was a problem with the form and nothing on your end, the form didn't recognise your SteamID as it is a digit shorter than most but the form has been fixed to recognise yours now and you can now post your appeal.