How can I simply upload files via API without manually generating an access token?

Hi playstationmobile,

As seems, it passed long time since you last used your application console to generate long lived access token. Years have passed since this feature has been deprecated and already dropped. If you have some long lived access token, it'll work still, but all new issued access token (it doesn't matter how exactly issued) are mandatory short lived (they have few hours live - typically 4 hours or so).

You can still have long term access (in similar way as has been before), but you need refresh token (one more in addition to access token). The refresh token is long lived and doesn't expire itself. For a possible way (one of number of options) to receive and use refresh token, you may take a look here. Just implement the steps in your application' workflow and all should look the same as before. 😉 You will need to implement in the application the last (repetitive) step only, where new access token will comes up as result of refresh token usage. If you're using some of official Dropbox SDKs, the only thing you need is proper client object initialization with everything needed (including refresh token, app key, and optionally app secret - optional when you used PKCE OAuth flow otherwise mandatory). Dropbox SDK has implemented the last repetitive step already, so you don't need to change anything more; just continue using your code as before.

Hope this gives direction.