Opportunities can have multiple states for sign up. When an Opportunity is either Closed or Full, you will not be able to interact with the sign-up button to join the Opportunity. To get more information on the sign-up state of the Opportunity, you will want to contact the manager directly.
Some Opportunities only allow signup for members of that Opportunity’s Organization. If you are not a member of that Organization, the signup process stops and a message opens prompting you to join the Organization first.
