Hey everyone, I am leaving this comment as a note to anyone else that encounters this issue. When using the Shopify app Express template, it uses an outdated version of the Shopify OAUTH protocol.
It took me a long time to find any information on this, but I found another post in the community that shed some light on this situation:
According to the post above, Shopify is no longer maintaining their official express template. So what that means is that we need to take the time to understand how to make this work with the Shopify API library that Shopify maintains for NodeJS.
It seems like that is actively being maintained so it’ll be much more reliable than the Express Template.
Shopify now recommends that we use the Shopify CLI to set up a managed Shopify Installation to keep track of our app configuration settings and to use a Token Exchange to handle OAUTH
You can find more information about this by reading the post I linked to above.