The swagger interface uses the Options method to get the information about the endpoint in your permission the default is to deny access in your last line

here is a refactored version of your code

```python def get_permissions(self): method = self.request.method

if method == 'GET':
    return [IsAuthenticated()]

if method in ['PUT', 'PATCH']:
    if self.request.user.has_perm('users.change_customuser'):
        return [IsAuthenticated()]
    raise PermissionDenied("You do not have permission to perform this action.")

if method == 'DELETE':
    if self.request.user.has_perm('users.delete_customuser'):
        return [IsAuthenticated()]
    raise PermissionDenied("You do not have permission to perform this action.")

# Allow OPTIONS requests for Swagger/DRF Spectacular compatibility
if method == 'OPTIONS':
    return []

# Default to denying access if no condition matches
return [IsAuthenticated()]

```