From 6th April 2023 all employers except those digitally excluded will be required to submit and amend P11D and P11D(b) forms online ONLY. Any paper forms will be rejected.
P11D's are used to declare benefits in kind to HMRC that employees/directors receive from their employer. These are benefits which are separate from the employees wages and must be declared yearly. For example, company car, healthcare etc.
For more information please visit: https://www.gov.uk/guidance/how-to-complete-forms-p11d-and-p11db#overview