When you select the Self Assessment client type and you go to the Secondary contact section you will see this message. For SA clients, the Secondary Contact is for your reference only. The contact will not be able to access this client file through the portal. 

Only the Main Contact can have access to the Client file on their registration, the secondary contact cannot register for the client portal and have access to the SA client file.

You can enter the details of the Secondary Contact but these would only be for internal use only. 

If you have a Scenario where the Self Assessment Client is Vulnerable or has a power of Attorney and you need them to have a Secondary contact who needs portal access then we do have a work around. 

• Set the Client type as a Trust. 
• This will allow you to still select the Self Assessment Tax Return service
• You can add the Main Contact as the Client 
• You can add the Secondary contact and have them register for the portal and have access to the Client file. 

If you want to keep the Client File as a Self Assessment client type then you can create a new client file for the Second person. 

• Create New Client 
• Set Client type as Other  
• You can get the person to register for the portal 
• You would need to upload documents to both the SA Client file and this new Other Client file so both parties can view what it is you want them to see or sign