Hi @Anonymous ,
Have you logged in with your powerapps account successfully?
Based on the error that you met, I think you didn't import necessary PowerApps modules successfully within your PowerShell window and log in with your powerapps account successfully.
Please follow my steps:
1)Run PowerShell as an administrator.

2) Execute the following commands firstly:
Set-ExecutionPolicy -ExecutionPolicy RemoteSigned -Force
dir . | Unblock-File
3). Import necessary modules:
Install-Module -Name Microsoft.PowerApps.Administration.PowerShell
Install-Module -Name Microsoft.PowerApps.PowerShell -AllowClobber
4)Add your PowerApps account:
Add-PowerAppsAccount /* <-- Open a dialog to provide your credentials */
Please notice that if you want to run this Get-AdminPowerAppConnection command, your account need to be admin of your talent.
5)run this command:
Get-AdminPowerAppConnection
Then you will get all the connections information of your talent.
What's more, only premium license of powerapps (per app plan/per user plan) could use this command.
Best regards,