Amazon flex substitute

My partner has an amazon flex account which he sometimes uses to deliver parcels. He earns under £1000 a year so does not need to do self assessment. With amazon flex you can use a substitute a driver to do a shift and then the account holder has to pay the substitute. I want to be his substitute as he cannot work that many extra hours as he has a full time job. So under his amazon account he will get earnings but will transfer to my bank account the money i earn. Will he need to a self assessment or will i? I will potentially earn over £1000 a year. How will hmrc know that i will work and not my partner? I don't want him to file a self assessment as he doesn't want to pay unnecessary accountant fees for filing accounts. When hmrc recieve income details from amazon via the digital tax rules they will potentially see that he may have earned over £1000 but in fact it will be me who earned as his substitute.

Hi Km2024,
As the money is paid to him, this brings the turnover above the £1000 limit and a tax return will be reqauired.
Te money he then pays to you will be classed as wages that are paid out to reduce any profit.
You will then need to declare the wages you receive as income too, in a tax return.
Thank you.