Hey tuffytutu,
It's awesome that you're making full use of QuickBooks Online's multi currency features. These were built to simplify the bookkeeping involved with your international business, while continuing to take advantage of the full potential of the advanced tracking for your accounts receivable. I'll be happy to help get this sorted.
When you create a new supplier, the system designate a part of your Accounts Payable specifically for them. You've most likely noticed that you have an A/P account for each currency. This is helpful as it lets us easily keep track of the exchange gains or loss to further enhance your reports. To ensure full consistency with this, the easiest way to change a supplier's currency is to recreate them with the correct settings.
I've got your back, so let me know how this goes.
