I'm Canadian but live in Ireland. Had the same problem and contacted admin. Got this:
"As part of integrating with the SportsHub payment system, we no longer
accept credit cards from outside of the U.S. and Canada. That's mainly due
to the new European GDPR law that went into effect, as we're not currently
compliant with it.
However, you would normally have the option to pay with Paypal, which should
work fine for those living overseas. Unfortunately, that option is
temporarily gone while we wait for Paypal to approve us."
I still have an account and card in Canada so was just able to use that. Otherwise you need a PayPal account.