Fixed pricing for ads on my app

I have an app I am about to launch in the mental health nice with a decent following on social media. I am going to have a therapist directory in my app and I’m wondering if I could have any success charging therapists a small fee (5-10 dollars a month) to be included in my therapist directory. There will also be a therapist spotlight card on the home tab in my app (Haven’t figured that pricing out yet thought)Instead of doing something like CTR pricing, I was just thinking about charging a monthly cost for the ad space aka being in the directory. Mainly because the app is new so I don’t expect to have hundreds of thousands of users clicking on the therapist links all the time so I’m not sure I would generate much revenue using CTR at first. However as the app grows after I make some money to use for running ad campaigns and I get more users maybe it makes more sense to use a CTR strategy. Thoughts?