Income Tax Refund - online Form Error

I have been having trouble applying for reimbursement of income tax on professional and subscription fees, using the online webform. I get an outcome letter from HMRC that the entered employer reference number is invalid. The issue is, that this is totally physically impossible from my part. There is no place where the online form asks for this information at all. https://www.access.service.gov.uk/login/signin/creds After the initial sign in through government gateway it does not ask for this information at all. Spoke to HMRC agent on phone while having for wait fo 1 hours+ to discuss this. Person on phone did not know how to help. Please can someone some sense into this, am I missing a step (I have gone over the steps again and again but cannot find any part where employer reference number was requested)? Thank your replies.

Hi Ana,
To claim for your professional subscriptions online, please see guidance here:
Claim tax relief for your job expenses
If unable to claim online you can submit your claim by post or by phone:
Claim tax relief for your job expenses if you cannot claim online
Thank you.