on Just Publishing Advice:
New authors, beware of vanity publishing companies and experts making you offers that are too good to be true
Have you received an email or social media message from an agent or publisher offering to publish your book?
If you are an author, you may have received a lot of them. On average, I get at least one per week.
Because indie authors are active on social media, it is easy for a predatory publisher to get your contact details. Then come the offers for their publishing services.
When publishing companies make you an offer that includes the word free, it is a signal that you should be very suspicious.