There is no tax to pay on the first £1k of trading sales.

If your sales as a Sole Trader are less than £1k you do not have to declare this income on your Self Assessment.

If your sales are more than £1k you must complete Self Employment pages on a Self Assessment but instead of deducting business expenditure from sales to arrive at a taxable profit, you can elect to deduct the Trading Allowance of £1k.