Someone asked Off Topic this question but I fear it's received little attention because the sub-forum wasn't the right one. The following answer can help you avoid an increasingly common form of misconduct:
A paper mill is used as an analogy with a factory where paper is made. In the sciences, scientific papers can be produced in large quantities dividing the labor needed to produce such a work by the number of co-authors you collaborate with. Reducing the effort you put in will increase your production but at the expense of reducing the merit you can claim for your papers. There is also evidence that the higher the number of co-authors, the lower the quality of papers.
The ONLY legitimate reason for co-authorship is to increase the probability of scientific findings, NOT to increase the number of papers published.
An extreme case is this one in the UK:
Mark Grffths: the professor who publishes a paper every two days
https://www.timeshighereducation.com/news/mark-griffiths-professor-who-publishes-paper-every-two-days
And in continental Europe:
IPAG (France), playing by the rules or tampering with peer-review?
https://www.econjobrumors.com/topic/ipag-france-playing-by-the-rules-or-tampering-with-peer-review