API Gateway regional custom domain name not resolving

I am attempting to take my API Gateway endpoint and map it to a custom regional domain name. Can someone help identify if I've made a mistake anywhere along the way? I've followed the documentation pretty faithfully but cannot pinpoint where I've gone wrong. I performed the following steps:

1. Used Route 53 to register a domain, let's say mydomainname.com.

2. Created a certificate through ACM with api.mydomainname.com, mydomainname.com and example.mydomainname.com included as CNAME records to the DNS configuration for my domain.

3. Created a custom domain name in API Gateway for my playground-api API with stage development (see below):

4. Using the Target Domain Name specified in the above image, went to my Route 53 Result Record Sets and added it in as a target:

When I attempt to access GET https://api.mydomainname.com, I get a CONNECTION REFUSED error. However, using the endpoint from the deployed stage (the endpoint provided after you deploy a stage) through API Gateway works perfectly.

The available endpoints I have exposed and deployed on API Gateway are GET /, PUT /widgets/, and GET /widgets/{id}.

I acknowledge there's been plenty of posts (like here, here, here, and here) on this topic, but it doesn't look like anyone has come to any good solutions yet. However, it appears the common theme in all of the posts so far are lack of enough details, so I hope perhaps my post contains enough information for more experienced SOers to help.