.Net API SDK - Best way to connect to a Business Dropbox?

This error message indicates that the access token you're using is for a "Dropbox Business API" app, which connects to entire Dropbox Business teams, but the method you're trying to use is for specific Dropbox accounts. 

If you want any kind of Dropbox account (Business or not) to be able to connect to your app, you should instead register a "Dropbox API" app. That kind of app needs to be authorized by each end-user, at which point the app receives an access token for that user's account and can call methods like GetCurrentAccountAsync without additional configuration.

Alternatively, if you only want to connect Business accounts, you can use your "Dropbox Business API" app registration. That kind of app only need to be authorized by a team admin, at which point the app receives an access token for that entire team. Your app would then need to additionally specify which team member to operate on when making an account-specific call such as GetCurrentAccountAsync. You can do so by first making a DropboxTeamClient object and calling DropboxTeamClient.AsMember with the relevant team member ID to get a DropboxClient for that team member.

I have been trying to use the AsMember method and it seems to always throw this error when I use it - "Invalid select user id format"

DropboxTeamClient teamClient = new DropboxTeamClient(OAUTHTOKEN);

var results = await teamClient.Team.MembersListAsync();

string memberID = string.Empty;
foreach (var member in results.Members)
{
    if (member.Profile.Email.Equals("tcash@mac.com", StringComparison.OrdinalIgnoreCase))
    {
        memberID = member.Profile.AccountId;
        if (memberID.StartsWith("dbid:", StringComparison.OrdinalIgnoreCase))
        {
            memberID = memberID.Substring(5);
        }
        break;
    }
}

var dbx = teamClient.AsMember($"dbmid:{memberID}");

The member ID I get from the member profile is in the format of "dbid:XXXXXX", while the code I have found in the forms seems to want to set it as "dbmid:XXXXXX".  I've tried both styles and neither worked.

The AsMember method expects the "team member ID", which is the ID that starts with "dbmid:". Dropbox supplies these values directly, and you should not attempt to modify them.

The team member ID is available as MemberProfile.TeamMemberId (not MemberProfile.AccountId).

Ok, so I did try using that value and it gave me the same error.

Can your share your current code for that? I just modified your earlier code and it worked fine for me:

DropboxTeamClient teamClient = new DropboxTeamClient(ACCESS_TOKEN);

var results = await teamClient.Team.MembersListAsync();

string memberID = string.Empty;
foreach (var member in results.Members)
{
    if (member.Profile.Email.Equals(EMAIL_ADDRESS, StringComparison.OrdinalIgnoreCase))
    {
        memberID = member.Profile.TeamMemberId;
        break;
    }
}
//or use MembersGetInfoAsync to look up a specific member directly

var dbx = teamClient.AsMember(memberID);
var result = await dbx.Users.GetCurrentAccountAsync();