You've got me here to provide some information about creating a Contra entry with different currencies in QuickBooks Online.
To process Contra transactions, you'll need to create a journal entry. However, being able to record a journal entry with different currencies isn't available. All customer and supplier transactions should be recorded in the currency assigned to them. Otherwise, you'll get an error.
There are three options on how you can track the entry. First, is to manually convert the one currency to another using the exchange rate. After that, add a memo indicating the actual currency you've received.
The other options are to make a duplicate customer or supplier to utilize a second currency and to create a home-currency wash account to move the currency from one account to another. Please see this article for complete details on how to accomplish this goal: Working with multiple currencies in QuickBooks Online.
Lastly, here are some links that you can visit, which provides insights about deleting and fixing currencies issues with journal entries in QuickBooks Online: