The installation link for this app is invalid (authorization code grant manually)

[lucas-neonblue]

Hi Shopify Community,

I'm encountering a consistent error when attempting to install an app on a test shop. The error message states: "The installation link for this app is invalid. The link for installing [app] cannot be used. Contact the app developer for more information."

Attempted Solutions:
* Followed Shopify's official implementation guidelines
* Used Handshake (an open-source OAuth framework for multiple platforms)
* Developed a basic server implementation with @Shopify/shopify-app-express and set up an /install endpoint utilizing shopify.auth.begin()

All implementation methods result in the exact same error message. I'm using the Authorization Code Grant OAuth flow since this is not an embedded app.

Has anyone else faced this particular error? Are there specific requirements or configurations that might be causing this issue?

Any insights or suggestions would be greatly appreciated!

Thanks in advance.