Hi @Jonathon_Minard,
Moving forward all apps will be created and managed via the Dev Dashboard, whether that’s Partner Apps, or Merchant Apps.
For the process that you’ve mentioned, with the merchant creating the app in their store admin directly, this is now replaced with the merchant logging into their Dev Dashboard to create the custom apps. This process is explained in the Shopify.dev documentation:
Any apps created this way, by a Merchant specifically, does not need an app review, and do not need any custom UI. Those requirements are specifically for public apps created by a Partner in the Dev Dashboard, that will be listed on our Shopify App Store directly. They do not apply for custom apps created by Merchants or Partners in the Dev Dashboard.
Here’s some documentation with more info on App Distribution Methods, also it’s good to know that merchants can only create custom apps, they’d need to be logged into a Partner Account in the Dev Dashboard to be able to create a public app that requires the app review previously mentioned.
One further difference that you will notice with this new workflow, is that the access tokens are not immediately available like they were when the app was created in the Admin.
New apps created via the Dev Dashboard, will need to use the new Client Credentials Grant workflow to generate an access token your app can use.
This means, when the merchant creates the app in the Dev Dashboard, they will need to provide you with the Client Id and Client Secret displayed under the app settings in the Dev Dashboard, then you can use those credentials to generate a new access token with the POST https://{shop}.myshopify.com/admin/oauth/access_token HTTP Request.