Oh yes, I do have IAP. I wanted to add additional payment options. I don't think it has anything to do with helping small companies. It has to do with person reviewing the app who probably doesn't understand what app does. As far as I understand if app is a marketplace then it can have other payment options as per Apple's guidelines.

I've added Apple Pay which users can use to buy credit and use it to connect with experts to get advices. We don't earn money from this credit purchase. Advisors pay us commission to use the platform. Other apps where they have allowed Apple Pay offer exact same features. Below is the rejection message. Guideline 3.1.1 - Business - Payments - In-App Purchase In-app purchase gives developers the flexibility to support a variety of business models in their apps. However, your app unlocks or enables additional functionality with mechanisms other than the App Store, which is not appropriate under App Store Review Guideline 3.1.1. Specifically, your app uses Apple Pay to unlock or enable Credits. Next Steps It would be appropriate to remove these features from your app and any other feature that unlocks or enables functionality with mechanisms other than the App Store.  You may also consider making this unlocked content available to your users as in-app purchases. Resources Learn more about our policies for apps that offer paid digital content and services in App Store Review Guidelines 3.1.1 and 3.1.3. Please see attached screenshots for details.