Who makes it
In the ordinary procedure, the application is filed by the employer. Before you start working, ask for a copy of the document and verify that the employer, position, period and conditions match your work.
When a separate authorization is not required
There are exemptions and other forms of admission to work: for example, rights under a certain residence status or a special procedure for Ukrainian citizens. Therefore, first establish your grounds, then discuss the document with the employer.
The main error
Neither the signed contract nor PESEL automatically legalize the work. When changing employers, the old permit cannot simply be transferred to the new company.