Currently the SDK builder doesn't allow users to choose the required parameters for downloading a SDK, and returns the error "Please wait for the Middleware Selector to load.".
The error reponse from one of the endpoints is: "message: "Domain is not a subdomain registered with this API Key".
Thank you for the report. Are you still facing this issue? I tried to download and SDK and Middleware Selector worked as expected, maybe there was a problem with our servers at that moment.
The problem has been solved since yesterday, and I was able to successfully generate a new SDK package.
My best guess is that it was indeed a server problem, which caused the problem with the Middleware Selector.