After completing App Info section and Building Blocks section (as i understand App homepage url and Redirect URI should not be fully functional yet), and after selecting Data client touchpoints (the app will use REST API) i am clicking Create App button
Yes, it worked. Looks like it was exactly the HTTPS requirement.
Will be great if errors will have specific reason mentioned in error body, explaining what specifically went wrong.
Thank you for your help!
Regards, Max.