Youtube API not working with 2.6

Youtube says following at https://youtube.com/my_profile_blogs_add

* WordPress Self-Hosted: Requires an API key and the API URL (https://your blog’s URL/xmlrpc.php).
Blog Service: [I choose: WordPress Self-Hosted]
Username: [I tried my self-hosted username and my WordPress.com username]

Password: [I tried my self-hosted username and my WordPress.com username]

API URL: [I enter https://myselfhostedblog.com/xmlrpc.php%5D

API Key: [I tried to type nothing and to copy and paste the API key from my WordPress.com dashboard]

Other threads on this forum says one should register on wordpress.com for an API key, other threads say to not enter any API key information. Any way I try it Youtube outputs:

An error has occurred. Message: Unknown

Could someone update this page https://faq.wordpress.com/2005/10/19/api-key/ with info about how to do this API key thing with Self-Hosted WordPress installs once this is resolved so there won’t be any more people asking for how to solve it in this forum? That is the only page Youtube links to from https://youtube.com/my_profile_blogs_add with information about the API key which they say is required for self-hosted WordPress blogs.