Vendor that I have a running balance with and paid with credit card

Hi there,

I have a vendor who I only pay with credit card and have a running balance with them. I have reconciled my credit card with my bank account just fine. However, I am not able to capture the HST I am paying as the "payments" that I send to the vendor is to buy "credits" to buy postage. Now depending on where the shipment is going, the tax are different respectively. I think I have to add an example, let's say:

I paid $30 to the vendor (which will show the $30 on my reconciled credit card)

then $9.50 is for the postage fee

tax is $1.23, so total bill is $10.73

My credit is $30-10.73=$19.27 (this will remain in my vendor account)

How do I show this since I am only showing that I expensed $30 on postage? Do I create a separate "bank" account for this vendor? If so, how do I post the transactions on this bank as? How will it tie back to the credit card?