I hope your day is going well so far. Since you're wanting to pay a bill for a vendor, then I recommend looking into the multi-currency feature within QuickBooks Online. This feature is used for owners who have customers, vendors, or bank accounts that use foreign currencies. You can check out the link above to see if turning on the multi-currency option would be best for your business. If you've decided to continue with this option, here's how to turn it on:
Learn more about managing your currencies through this link.
Keep me updated about your decision and if you run into any trouble along the way. Enjoy the rest of your day!