How to categorise a transaction that's been split on 2 different accounts with 2 different currencies against a supplier with its own currency?

Let's find out why you're getting an error so we can fix this, Akmenutrit.

This error happens because of the mismatch of currencies of your suppliers and transactions. You'll want to use the Transfer option or exclude the transaction instead. To exclude: 

1. Go to the Transactions tab and select Bank transactions.
2. Mark the checkbox of the transactions to exclude.
3. Click Exclude.

Once done, the transaction moves to the Excluded tab of the Bank Transaction page. You can manually enter the transactions with the same currency to categorise them correctly. 

Moreover, learn how to reconcile your account to compare each transaction with the ones entered into QuickBooks and if everything matches your balance accurately. I've added this article for more details: Reconcile An Account in QuickBooks Online.

You can always reach out to us if there's anything else we need to do to help you. We're here to assist you further.

Yes but if I use this solution, I will never be able to deduct the funds from the currency they were taken correct? 

Hence I will always have a huge discrepancy on my bank account for this specific currency?

What is the workaround? I can't believe I'm the first in this situation?

Or just recording a transaction for a supplier in USD Currency, while I paid with CHF and my home currency is GBP?

Thank you for getting back on this thread, Akmenutrit.

In QuickBooks, we cannot associate one vendor profile with multiple currencies. However, you can create a separate profile for the same vendor and assign the appropriate currency to each profile. This way, you can transfer the funds to the correct currency.

Here's how:

1. Navigate to Expenses and then Vendors. 
2. Click on the New button. 
3. Choose a different currency in the Currency field. 
4. Enter the vendor's name, making it slightly different by adding extra or special characters. 
5. Finally, click Save.

You can read this article for more information about adding vendors with foreign currency: Add a vendor with a foreign currency in QuickBooks Online.

Additionally, I'll share with you these resources that may come in handy: 

• Assign a foreign currency to a customer in QuickBooks Online
• About Multicurrency

If you have any further queries or issues regarding vendor management in QBO, let me know by tagging me in your response. I'll be happy to help you out promptly. Have a wonderful day!