Elizabeths thanks for your question! This is quite the use case! 

The issue with a shared inbox is that it doesn't have a set of credentials (Specifically a password) that can be used to connect it as a channel.

However, in theory, it is possible to "reset" the password for it, thus creating a password you can use.

1. Go to the Microsoft 365 admin center and sign in with your admin credentials.
2. Click on "Users" and then select "Active users"
3. Select the shared mailbox you want to set a password for.
4. Click on "Reset Password"

Bear in mind, our devs have not tested this workflow, but it should work. You can try connecting this way and if you do, let us know in a comment how it works! 

Thanks for your question!