Can you please clarify with me, is this for the Power Up Challenge?
 
Also, if not, is this a real developer environment, or an environment (sandbox or prod) that you are calling a Developer environment?
 
Can you please also share, are you attempting to get there via the Maker Portal, or via Power Automate portal?
 
I am asking because, you can also attempt via Copilot studio and select Development, but need more information as we need to get you into at least the Default environment to try to resolve it.
 
 
If not, and we cannot get you into your environment you will need to open a ticket with Microsoft.
If these suggestions help resolve your issue, Please consider Marking the answer as such and also maybe a like.
Thank you!
Sincerely, Michael Gernaey