Hello, 

I can not add a class because I do not create the transaction myself. It is created automatically when there is a payment in different currencies. 

For example, on the picture attached to this message, you can see that my company received 15 712.11 EUR. When we recorded these payment to the related invoice, an entry of 546.67 USD was created to record the rate difference on this account " 666100 Gain/Loss on exchange rate". I am unable to add a class, even when I try to click on the transaction. By clicking on the amount,  QBO sends me on the invoice payment entry (as on the screenshot) and not to the 546.47 USD entry so I am not able to add a class or change the account. 

How can I fix that? 

Many thanks,