Why does the option Add Link is not being displayed on any activity?
Oracle Field Service (OFS)
Users no longer see the option "Add link" in Links tab for any activity. The parameter Supports of links" is checked in the Activity Type and users have the correct permission to add links to an activity. Users should be able to add links.
It is possible that a user set the Link Template(s) to inactive by mistake causing the Add Link button not be available (since there are no link templates to be used).
Go to Configuration > Link Templates and verify if the template(s) are listed. If the templates are missing, go to View and uncheck the filter "Hide inactive templates". Click Apply. Locate the link template(s) you were using and click Modify. Select the 'Status' checkbox to reactivate the link.
Existing activity link types cannot be removed from the system but can be deactivated/activated by a user that has read-write access to Link Templates screen.