Redirect uri didn't work on shiny server

I am new to using OAuth 2 with Dropbox.

I deployed a shiny app on the shinyapp.io server.  The function only tests if I can upload a file to Dropbox.

I tested the app on my local machine, and it worked well. However, when I deployed it on the shinyapp.io server, I set redirect uri as: "https://qml-lab.shinyapps.io/05_merds/oauth2callback/"

My Dropbox app's OAuth 2 redirect uri is also the same.

However, when I try to get authorized, the browser doesn't open the authorization page, and my app log only shows the following log while just waiting:

2025-02-25T05:00:42.706101+00:00 shinyapps[14070350]: Please point your browser to the following url: 2025-02-25T05:00:42.711022+00:00 shinyapps[14070350]: "https://www.dropbox.com/oauth2/authorize?client_id=<My ID>&redirect_uri=https%3A%2F%2Fqml-lab.shinyapps.io%2F05_merds%2Foauth2callback%2F&response_type=code&state=pg0LzPqOZv  "I tried to open the above address manually, but it shows Not Found.

Can anyone tell me what the problem is?

Thanks,

Kuo