You've just built an awesome API as a product and want your customers to easily understand and explore its features? This will certainly make you wonder how you could best provide documentation about this API to your customers.
On first publication of our ship-data and analytics APIs we hit this question as well. After a quick research about available solutions we opted - due to a lack of other options - for the official AWS API Gateway Developer Portal.
Fast-forward: Not only did we have a hard time customizing the portal but AWS informed us about a severe security issue inside the portal which would force us to migrate to a newer version. Migration, however, was such a nasty experience, that we took this as a reason to search for better and easier maintainable solutions.
This was the trigger for coming up with our current solution. A stupid simple and yet fully serverless portal to document your public facing APIs - and all of this beautifully. Check it out at https://docs.hoppe-sts.com.