Getting "Something went wrong" when installing custom connect app for BitBucket

Hi
I am following these steps Install an app from your site and the Getting Started steps with a custom app that is online, and not locally via the npm install.
On going to Log in with Atlassian account, I get this “Here’s the error we encountered - an addon_key is required for this application.”
SO I then add &addon_key=testing to the end, then I get “Something went wrong”
I also go to Installed Apps, Development mode is already on. I click the add from URL link and it also states “Something went wrong” there after I removed it from Develop Apps because it first stated “Invalid request. This app-key has been registered for a different descriptor url. Please contact the app vendor for help.”
Please advise where I am going wrong?
Thank you
Yatish

Hi all. Any idea please? Thank you