Ungoogled Chromium: Dropbox setup fails: "Invalid redirect_uri"

### Which version of floccus are you using?

5.10.2

### How many bookmarks do you have, roughly?

200

### Are you using other means to sync bookmarks in parallel to floccus?

no

### Sync method

Nextcloud Bookmarks

### Which browser are you using? In case you are using the phone App, specify the Android or iOS version and device please.

ungoogled chromium

### Which version of Nextcloud Bookmarks are you using? (if relevant)

_No response_

### Which version of Nextcloud? (if relevant)

_No response_

### What kind of WebDAV server are you using? (if relevant)

_No response_

### Describe the Bug

The title says it all. I try to setup using dropbox and I get that error.

### Expected Behavior

It should not give an error.

### To Reproduce

Try to setup using Dropbox and ungoogle chromium

### Debug log provided

- [ ] I have provided a debug log file

Start by reproducing the Dropbox setup flow in Ungoogled Chromium and inspect the redirect URI sent during authorization. Compare it with the URI Dropbox expects; done means Dropbox setup completes without the “Invalid redirect_uri” error, with a debug log or equivalent reproduction details to verify the fix.

Written by the indexing model from the issue text.