Good day,
As i decided to dive into extensions, and after reading the guidelines / documentation about it, i wanted to create an extension.
When going on my dashboard, i am unable to register an extension.
I get the button unclickable with a message “you don’t have permission to create extensions”.
Any help?
Hello.
Same problem, waiting for replies in this thread 
Hello here,
I resolve this problem by completing the OnBoarding process in my dashboard just here: https://www.twitch.tv/YOURUSERNAME/dashboard/settings/payout-onboarding
Do not forget to replace YOURUSERNAME by your user name 
Grettings
@Kemetos, Thanks, No luck though however, that’s a “I’m sorry, that page is in another castle!” page :] Still no permissions.
I signed up and completed on-board last night, a few hours later I am now able to create extensions via https://dev.twitch.tv/dashboard/extensions
Looks like you just have to wait for either a final approval or for some caching to catch up.