If you receive an error notification in the bell section of Portal while attempting to upload the student loan deductions file, it's due to the file containing both SL1 and SL2 types.
Please contact HMRC and inform them that the uploaded file includes both SL1 and SL2 types. Request a new file that contains only one type.
The software has been designed to accept only the specific content required by HMRC instructions either SL1 or SL2, based on your selection.