the Online Services Helpdesk to ensure that HMRC has your correct address and postcode. to have registered for HMRC Online Services and enrolled for the PAYE/CIS for Agents service (see the section above to find out how to do this) your client's employer PAYE reference and Accounts Office reference the authorisation code HMRC will send to your client by post - the code with 'PE' for PAYE and 'CS' for CIS Please note: The authorisation code can take up to seven days to arrive. You will need to enter the code before the client appears on your client list, so ideally you need to do this well in advance of a filing deadline. You must enter the code within 30 days from the date on the letter, otherwise it will expire. Filing CIS returns for your clients Any agent can file a return for CIS on a client's behalf, even if they're not authorised with HMRC for CIS matters. However, if you want to file your clients' verification requests online using the PAYE for Agents service you need to be authorised to do so (see the sections above for more information). But as a 'filing only' agent you won't be able to correct an error on a return or undertake other services like verifying subcontractors unless you're authorised. And HMRC's free CIS software doesn't support filing only agents, so you'd need to use commercially available software. Online administrators and assistants The first person to set up your HMRC online agent