Thanks for the additional information. In that case, it's likely due to a restriction that can be set on Dropbox Business teams that prevents links from being accessed outside of the team.
By default, these links are accessible without authentication, but Dropbox Business team admins can optionally enforce additional access controls on links for their users in general, which also apply to the links as returned by the Chooser. You can find more information on this restriction here:
https://www.dropbox.com/help/504
You can detect the failure to access the file content via these links using the status code they return. (I.e., 200 would indicate success, and 4xx, in this case 403, which indicate failure.)
Unfortunately, we don't have a good solution right now for using the Chooser from accounts that are part of Dropbox for Business teams where the admin has enabled restrictions on shared links like this, but I'll send this along to the team to look into how to potentially improve this.
That being the case, one alternative right now is to use the HTTP API instead, where the /files/download call isn't subject to the same restrictions as the authorized access token allows you direct access to the user's account:
https://www.dropbox.com/developers/documentation/http/documentation#files-download
That would be substantially more work to implement though.
