You can expense up to £500 in fees or interest you paid to your bank in running your business. Most sole traders are unlikely to go above this allowance.
If your bank fees are significantly higher than £500, it may be worth moving away from cash based accounting (the way earnr does things) and onto the more complex accruals basis.
That said, it's unlikely that many sole traders, and particularly side hustlers, would see fees over that level.