Once SendBoard has been added to a Trello board for a given team, anyone who is part of that Trello team and has access to the board should be able to use SendBoard features.
We've listed some reasons why features might not be showing for certain users.
SendBoard is not authorised
One possible issue is that the 'Authorise SendBoard' step was not completed correctly. To verify this, open the Trello board and refresh the screen in your browser. If authorisation is not yet completed, this would prompt the steps to authorise SendBoard to work with Trello.
See also: Troubleshooting SendBoard authorisation
They're a guest user on the board
Another possible issue is being a guest users on the Trello board, and not a member of the Trello team. The user would need to be added as a member of the Trello team in order to access SendBoard features.
The board is not under a Trello team
If your board is not part of a team, but you want other Trello users to have access to SendBoard features, you can create a team in Trello and move the board to be linked to that team. Creating a Trello team is a great way for teams to keep Trello organised.
Third party cookies are blocked
SendBoard requires that third party cookies are enabled on your browser. This is true for other Power-Ups like Butler too. Heres an article on Trello's help portal that explains how to enable third party cookies on several different browsers.