I want to add my spouse to my billing account.

Hi @ashucn, please read the stickied post on this subforum:

https://forums.xfinity.com/t5/Sign-In-and-Account-Management/Top-Identity-Troubleshooting-Steps-START-HERE-BEFORE-POSTING/td-p/3366881

Here's the section you need:

Invite someone to your account https://customer.xfinity.com/users/add-user

• You must be signed in as the primary
• This is very helpful if you want them to have their own sign-in credentials and to be recognized when they go to a retail Xfinity store. Make sure you assign them the right role.