Hi @Harvie
This should be fine. The main thing is that you would have a backing document with further details from the marketplace itself. The same concept could apply to eBay sales for example.
In fact, you could just put a description as “Weekly Sales w/e 26/01/2018” for example, and combine all weekly sales rather than using a new invoice for each sale.
When you tag a transfer from a USD to GBP bank account, QuickFile will prompt you for the equivalent GBP value.
With a sale on PayPal, there are a few things to consider. Firstly, where possible, use their exchange rate rather than the one on QuickFile as this is the one that’s been used for the transaction.
The other thing to consider is the PayPal fee itself. In short, you would have 3 bank entries for every 1 real one. There’s more on this here:
I hope that helps!