HMRC's got their softwrae wong
If you used it before 21 January to work out January claims for your employees that are not on a fixed salary you’ll need to re-calculate your claims if:
you used an employee’s pay for January 2019 as reference pay, instead of 2020, and
their pay was different in January 2019 to January 2020.
If you used your employee’s January 2020 pay you do not need to take any action.
HMRC ask that you please accept their apologies if you need to re-calculate your claim.
If after you have made your re-calculation you find out your claim was incorrect and:
you have claimed too much, you should amend this in your next claim or let HMRC know as soon as possible and make a repayment online, through our card payment service or by bank transfer – go to 'Pay Coronavirus Job Retention Scheme grants back' on GOV.UK.
you claimed too little, please call the helpline to amend this by 1 March.
Go to GOV.UK and search 'Get help with the Coronavirus Job Retention Scheme' for more information on how to amend your claim.