Facebook Groups Monetisation

I have 4 active Facebook groups about jobs search and hiring in 4 big cities in Canada. The audience is about 120k members and the engagement is quite good. I also have a Canadian job board website. I already pinned a post that promotes the website and another post offering advertising services directly in the groups. They were pinned for 2 weeks already and I am seeing only a few users visiting my website from Facebook and no commercial orders.

What am I doing wrong? What would you recommend to do instead?

Typically, your Facebook groups attract job seekers and job postings. They usually have their own channels to leverage to attract and recruit candidates. Your job posting isn't wrong because of pinned posts, but because you haven't approached them correctly. They usually operate for free and don't want to pay. If you want to charge and attract them, you can run ads or create a website; that would be more effective.

Such groups are often mistaken for free services, so participants are not yet accustomed to commercial offerings. You need to drive sales by proactively targeting small-scale recruiters first. once you achieve results with these smaller clients, other recruiters will naturally seek you out.