Best Services for API Monetization?

I've been asked to "productize" a private REST API for a side project, and thought it would be an interesting exercise. I'm looking for "API gateway as a service" (ideally with a thriving API store to help with discovery) rather than a self-hosted solution.

Here's what I've found so far:

• Amazon API Gateway: https://docs.aws.amazon.com/apigateway/latest/developerguide/sell-api-as-saas-on-aws-marketplace.html

• Azure API Management: https://docs.microsoft.com/en-us/azure/api-management/api-management-howto-add-products?tabs=azure-portal

• Google Apigee: https://cloud.google.com/apigee

• IBM API Connect: https://www.ibm.com/docs/en/api-connect/10.0.1.x?topic=SSMNED_v10/com.ibm.apic.apionprem.doc/tutorial_apionprem_monetization_offer.html

• Kong (or maybe not? articles mention "Mashape", which seems to be dead): https://konghq.com/solutions/create-a-developer-platform/

• Tyk Cloud: https://tyk.io/docs/tyk-cloud/

Before I dig into these further I'd really appreciate thoughts and guidance from HN devs who are doing API monetization.