Route "message_ui.add" does not exist.

Created a patch to solving the issue. Kindly review it.

@rahul17,

The route "message_ui.add" has existed since 2017, and probably longer.[1]

Instead of adding an update function, I think `message_ui_install()` should be update.

Instead of rebuilding the routes, maybe we just clear the cache?
`drupal_flush_all_caches()`

[1] https://git.drupalcode.org/project/message_ui/-/commit/19056871f8cd2c3c2...

🐛 JSON:API PATCH request wants permission that doesn't exist? Fixed will need an update function. I think we should clear the cache during the install, but also in the 8.1 update too.

Automatically closed - issue fixed for 2 weeks with no activity.