Hi,
The tax relief threshold is currently £60000 for incomes between £60000 and £240000. This means that the gross that you and your employer can pay into your pension pot is £48000 and the pension provider claim the basic rate tax from HMRC to bring it up to £60000.
If you have not used up to your threshold over any of the last 3 years, you can carry forward the surplus and apply it to your pension payments, to pay in excess of threshold and not have to pay tax. You can see the guidance here:
Check if you have unused annual allowances on your pension savings
Thank you