Troubleshooting
Nearly everything is one of the first four.
Nothing arrives at all
The environment is not on the list. environments defaults to ['production'], and APP_ENV on the machine you are testing is probably not that. This is the single most common cause.
Version 3 is installed. A bare composer require larabug/larabug installs 3.8, the last stable release. composer show larabug/larabug says which you have; installation has the command for version 4.
The keys are missing or wrong. Run php artisan larabug:test, which says which of the two it is.
The config is cached from before your change. php artisan config:clear, then try again.
One exception arrives and the rest do not
That is sleep doing its job. The same exception from the same place is reported once per window, 60 seconds by default. Lower it while you are testing if you need to see each one.
Everything arrives twice
Two things are reporting: the exception handler and a manual LaraBug::handle() call in a catch block for the same exception, or a larabug channel left in the log stack from version 3. Keep the exception handler and remove the other.
Queue jobs are missing
Check, in order: jobs.track_jobs is on, the queue is not in ignore_queues (or is in only_queues when that list is set), sample_rate is not sampling it away, and the worker has been restarted since your last deploy. A worker holds the old config until it is restarted.
The user block is bigger than expected
Without Larabugable on the model, the whole model is sent. User context is one method that fixes it.
Still stuck
Turn on report_sdk_errors while you are looking, which makes the client report its own failures rather than swallowing them, and check your application log for what it says. Turn it off afterwards.
If that gets you nowhere, write to us with the project key and roughly when you tested. We keep our own errors in LaraBug, so the report usually finds the cause faster than a description of it.