Without an App Catalog and a setting enabled, your users may run into the following error when attempting to access the SharePoint Store from the “Add an app” dialog:
“Sorry, apps are turned off. If you know who runs the server, tell them to enable apps.”
If you’ve run into this issue and are a farm admin, you can enable the app store and ability in SharePoint 2019 by following these steps. If you’ve already created the App Catalog site collection, skip to step 4.
1. Log onto your central admin server and open central admin
2. Choose Apps > Manage App Catalog. Make sure the Web Application shown is the correct web application then click OK to create a new App Catalog (or enter a URL for one if you’ve already created one)
3. Set the App Catalog site name and description, URL, admin, and then end users who should see apps in the catalog.
4. Once you have an App Catalog, go back to Apps > Configure store settings.
5. Confirm the Web Application shown is the correct web app, then change App Purchases to Yes. Save your changes.
Now when users who were granted access to view apps in the store choose SharePoint Store from the “Add an app” dialog, they’ll be able to get marketplace apps as well.