'Log in to Experience as User' in Salesforce Does Not Work on Manage External User Button on a Contact

The error shows up when the affected user profile is not added to the Experience Site Members list. 

 Please follow the below steps to resolve the issue:

 From Setup, in the Quick Find box, enter Feature Settings, and select Feature Settings.

• Go to Digital Experiences | All Sites.
• For your store, click Workspaces.
• Click the Administration tile.
• Click Members.
• To add members using profiles:
• To filter profiles, select a profile type from the dropdown menu. To search for a specific profile, enter a search term and click Find.
• Search returns profiles for the selected filter. 

NOTE Search results include profiles that are already part of the site.

• Select the user profiles you want to allow access to your site. To select multiple profiles, press CTRL.
• Click Add.
• To add members using permission sets:
• To search for a specific permission set, enter a search term and click Find.
• Select the permission sets you want to allow access to your site. To select multiple permission sets, press CTRL.
• Click Add.
• Click Save.

If the site is Active and welcome emails are enabled, users with the profiles or permission set you have added will receive a welcome email. The welcome email includes a username and a change password link if it’s sent to an external user who hasn’t logged in to a site yet.