From memory Beem it only works with MC & Visa so Amex is unfortunately not an option. Even then, not with all bank issued cards - for instance, I couldn’t register my Macquarie Visa but could use my Westpac MC. Official reason I was given was they have some sort of agreement whereas Macquarie does not.
I think with Post Billpay would only work if it’s an accepted payment method and if PayPal is an option. I’m sorry don’t know off hand if this billet can be paid by PayPal otherwise you might be in luck though the experience is that Amex is paying reduced points for government charges even if paid by PayPal so Sniip might be the only viable way to do it only with a fee.
I think with Post Billpay would only work if it’s an accepted payment method and if PayPal is an option. I’m sorry don’t know off hand if this billet can be paid by PayPal otherwise you might be in luck though the experience is that Amex is paying reduced points for government charges even if paid by PayPal so Sniip might be the only viable way to do it only with a fee.