when I use the business endpoint to create a team folder (in the legacy configuration of Dropbox), the team folder is created but it is not displayed in the home page, only in the admin console. When I check it in the admin console, I can see no members linked to the team folder. So I checked the API reference to see whether there is a method which would link the teams or members to the team folder but I was unable to find such method.
The/2/sharing/add_folder_member endpoint is a Dropbox API user endpoint, but you can call it using the same "team member file access" Dropbox Business API app viathe "member file access" feature. That's a way for Dropbox Business API app's with the "team member file access" permission to call Dropbox API endpoints by specifying a user or admin to operate on behalf of.
For example, in this case, you can add the 'Dropbox-API-Select-Admin' HTTP header and set it to the account ID of a team admin to make the /2/sharing/add_folder_member call.
Apologies for the confusion; I was overly broad in my earlier message. While you can use /2/sharing/add_folder_member to add individual members or groups to shared folders, for team folders in particular you can only add groups, not individual members.
If you try the above again, using the 'Dropbox-API-Select-Admin' header, but specifying a group ID as the "dropbox_id", instead of a specific member ID, that should work.