i code on QTCreator, i would like create an application for make a link between my deposit and the client. My question is, how i can use the API (or other solution) for creat the link between my app and my deposit.
For example, in my computer i have the file "tom.png" i would like upload on my deposit. For this, i open my application, i select my file and i click on the buttom "upload". But, i don't know how a do can this on background for send the document on my Dropbox.
Dropbox does offer an API you can use for listing, uploading, and downloading files, among other operations. You can find everything you need to get started with the Dropbox API, including documentation and tutorials, here:
The "<oauth2_access_token>" there is just a placeholder, and should be replaced with the actual OAuth 2 access token for the account. From the error message, it sounds like you're sending an invalid value for that (either the placeholder itself, or an invalid access token string). You should check what you're actually sending and correct it so that you're sending the valid OAuth 2 access token. You can find more information on how this process works in the OAuth Guide and authorization documentation.