IIt depends on your market. Which side will gain the most from using the app? If you help one side to gain more income there is a perfect place to have monetization strategy implemented. It could be a fee for the payment transaction (if you process payments) or some payment for completed project/class/etc.

If there is no payment in place you might consider making another profile level for either users or providers, giving this level features they are willing to pay for. Something that helps them save time or get some income as a result. It’s hard to say without more details about the app.

I won’t bother with regular ads, unless you can have some kind of partnership deal related to your niche. For example, if it’s an app for tourists/guides you might get a partnership with one of the airline ticker aggregators. Think about companies who can benefit more from ads for your app audience.