Hi
PayPal does not have a UK bank licence so their handling fees are not bank charges although they can be accounted for as such.
If I were you I would create a nominal account say 7907 and name it Selling fees, or use a “direct expense” like n/c 6900 Miscellaneous Expenses, as PayPal fees are taken directly from each sale made.
Either of these codes can be used for any selling fees like Ebay fees, Klarna fees, PayPal fees.
You could even phone the HMRC and ask them if it would be OK with them to use box 19 (Other allowable business expenses) on the self employment tax return for PayPal and Ebay fees