How do I pay my bill online with a foreign credit card that DOES NOT have a zip code?

For what it’s worth, I entered ‘00000’ as the zip code using a Canadian credit card and it immediately authorized. I made the payment two days ago, and it has shown up in the ‘posted transactions’ for my credit card -- so I think the payment has actually gone through. 

I previously tried doing a direct payment from my Canadian bank account, and while the payment initially authorized, it ended up not going through (and then my payment was overdue). So using an international bank account seems not to be the way to go.