A school creates an application. Do they need to sideload it using Marketplace?

The scenario is:

• A school signs up for Blackbaud Developer.
• They create an application.
• They go to the OAuth authorization URL to authorize it for their environment.
• They get an error: “This application has not been connected to your Blackbaud environment.”

Do they need to sideload the app through Marketplace even though they themselves created it? Or does this only when the school has multiple environments?

The docs say, “When you create an application, you have the option to make it available to other schools via the Blackbaud Marketplace" (emphasis mine). I'm wondering if Marketplace is still needed if the school is trying to make their own application available to themselves.