API File upload to a member's shared folder

Using the /2/files/upload endpoints (or /2/files/upload_session/* endpoints, for larger files) is the correct way to upload files.

When you do so, you'll specify the 'path' for where to upload the file. This would be the path in the connected account, based on the access token used for the API call. The path does not have to be inside a shared folder, but it can be. You can specify the path to be inside a shared folder, or not, depending on the use case, and/or user input, etc. 

Note that if the access token is for a particular, say, User A, but you want to upload the file to another user, say, User B, you would need to either:

• upload the file to a shared folder in User A's account that User B is also a member of
• get and use an access token for User B instead

Note that one exception is if you are using a "Dropbox Business API app" with the "team member file access" permission, in which case the access token enables access to the entire team and you have the ability to perform operations on any team member.

I recommend reviewing the Namespace Guide and Content Access Guide for more information.