How to add custom app to second store (multi-store enabled)

Hi, we have a custom app that now has multi-store enabled (plus stores from a single client), but it’s a bit confusing on how to create the install links

On the Partners Dashboard, inside the App’s distribution page Shopify provides the following template:
https://{shop}.myshopify.com/admin/oauth/authorize?client_id=#{api_key}&scope={scopes}&redirect_uri=#{redirect_url}&state={nonce}&grant_options={access_mode}

I filled in each section as instructed on this page but I keep getting the following error:

Oauth error invalid_request: Could not find Shopify API application with api_key

The server our app is running on has the proper .env variable values, so I am not sure why this is happening.

If anyone has any ideas / an easier way to install a custom app on a second store then that would be great.

I wish Shopify just generated another link for this second store like it did for the first store…