Sending the same kind of Job to the laravel Queue Worker

I am trying to send a job one at a time to the queue worker but Laravel Queue Worker is somehow executing the jobs at the same time. Based on the Laravel Queue documentation; it says the jobs execute asynchronously but in my case, it is not. So, I am not sure what's going wrong.

I also tried Job Chaining but it seems Job Chaining allows only different kinds of jobs.

My job's purpose is the same but for different customers.

I appreciate any sort of help.

I am using Laravel 5.6

via Chebli Mohamed