Django Abstract User Error in Using Permission

I am making a custom user model using AbstractUser in django.contrib.auth.models.

everything was working fine. and when i wanted to make some changes in user_permissions of my SiteUser then django gave error that SiteUser has no attribute named 'user_permissions'

then I thought of extending PermissionMixin in django.contrib.auth.models to my SiteUser class to make changes in 'user_permissions' but now It is throwing error like -

project.SiteUser.user_permissions: (fields.E304) Reverse accessor for 'SiteUser.user_permissions' clashes with reverse accessor for 'SiteUser.user_permissions'. HINT: Add or change a related_name argument to the definition for 'SiteUser.user_permissions' or 'SiteUser.user_permissions'. project.SiteUser.user_permissions: (fields.E304) Reverse accessor for 'SiteUser.user_permissions' clashes with reverse accessor for 'SiteUser.user_permissions'. HINT: Add or change a related_name argument to the definition for 'SiteUser.user_permissions' or 'SiteUser.user_permissions'. project.SiteUser.user_permissions: (fields.E331) Field specifies a many-to-many relation through model 'project.SiteUser_user_permissions', which has not been installed.

P.S. - I have used AUTH_USER_MODEL='project.CustomUser'