Immigration Health Surcharge Reimbursement

I have noted that for NHS workers, one can now claim back part of their IHS.
https://www.immigration-health-surcharg ... ce.gov.uk/

however i am getting an error when uploading payslips as evidence of employment, even if i upload the correct document in correct format.
"There is a problem
Select a file that is either a jpg, jpeg, bmp, png or pdf".

The question is, has anyone successfully submitted theirs?