Some or all of the below information will be requested if it isn’t supplied; for fastest response please provide as much as you can. 
The Basics
- Nextcloud Server version (e.g., 29.x.x):
Nextcloud 30.0.4
- Operating system and version (e.g., Ubuntu 24.04):
Rocky 9.5
- Web server and version (e.g, Apache 2.4.25):
Nextcloud AIO latest
- Reverse proxy and version _(e.g. nginx 1.27.2)
Nextcloud AIO latest
- PHP version (e.g, 8.3):
Nextcloud AIO latest
- Is this the first time you’ve seen this error? (Yes / No):
- Yes
- When did this problem seem to first start?
replace me
- Installation method (e.g. AlO, NCP, Bare Metal/Archive, etc.)
Nextcloud AIO latest
- Are you using CloudfIare, mod_security, or similar? (Yes / No)
- No
Summary of the issue you are facing:
I have instance A and instance B,
Instance A have user1 and instance B have user 2.
Both servers have each other as trusted and green (I ran occ federation:sync-addressbooks).
Issue 1
When I start type @use on instance A, I don’t see user 2.
The email for user 1 on instance A is user1@domainA.com, but Nextcloud is installed on cloud.domaina.com so a user need to type the whole user1@cloud.instancea.com, it still shows federated and email request in Talk:
Issue 2
Users tend to write the email address of the person (because it’s shorter I guess), but then it doesn’t work for the federation because it thinks it’s the nextcloud domain.
My email: user1@instancea.com, federated id: user1@nextcloud.instancea.com
It’s all very confusing. I thought I could search for all federated users and see a green icon or something to clearly show that this user can be federated, and not showing the option at all if the user is not found.
Can someone enlighten me on how this is supposed to work?
I also found out the hard way I cannot share a file with another instance and then start a discussion on that file over federation 
Kind of limit the collaboration possibilities 
Hope it’ll be implemented eventually 
Steps to replicate it (hint: details matter!):
- Create 2 instances
- Create a user on each instance
- Enable everything about federation
- Run
occ federation:sync-addressbookson both instances - Try to invite a user from the other instance
- Try to invite a user from an instance that doesn’t exists
Log entries
Nextcloud
Please provide the log entries from your Nextcloud log that are generated during the time of problem (via the Copy raw option from Administration settings->Logging screen or from your nextcloud.log located in your data directory). Feel free to use a pastebin/gist service if necessary.
PASTE HERE
Web Browser
If the problem is related to the Web interface, open your browser inspector Console and Network tabs while refreshing (reloading) and reproducing the problem. Provide any relevant output/errors here that appear.
PASTE
Web server / Reverse Proxy
The output of your Apache/nginx/system log in /var/log/____:
PASTE HERE
Configuration
Nextcloud
The output of occ config:list system or similar is best, but, if not possible, the contents of your config.php file from /path/to/nextcloud is fine (make sure to remove any identifiable information!):
PASTE HERE
Apps
The output of occ app:list (if possible).
Tips for increasing the likelihood of a response
- Use the
preformatted textformatting option in the editor for all log entries and configuration output. - If screenshots are useful, feel free to include them.
- If possible, also include key error output in text form so it can be searched for.
- Try to edit log output only minimally (if at all) so that it can be ran through analyzers / formatters by those trying to help you.