I know you're frustrated as I am because even if you follow the instruction on their link to resolve it, It just doesn't work. Before, they will provide you the two CName settings but now they're telling you a vague instruction aside to the bX- error you're experiencing.
So let's cut the ramblings and head to their hideous instruction there quoting the "Your domain must be properly registered first."
Making your non-Google Registrar Domain Properly Registered
Non-Google Registrar means, not bought at Google Domains. It could be sold at GoDaddy, or any other Domain providers. Here's what you need to do. Go to your Google Webmasters, head directly to this link [ https://www.google.com/webmasters/verification/verification ] and click 'Add Property' button. Add your Custom Domain there (see screenshot).
On Verification method, don't authenticate with your Domain provider even though it's already listed in the Selection, It will Fail. Tick 'Other' and do it manually (follow the instruction there).
Go to your GoDaddy's Domain Manager [ https://dcc.godaddy.com/domains/ ], and tick the three-dots icon of the Domain you want to configure, click 'Manage DNS' (see screenshot below).
Copy-paste the verification text from your Google Webmaster and also follow the instruction there. Apply it to GoDaddy's DNS setting, see screenshot:
After saving your DNS Setting in your Domain provider, head back to your Google Webmaster and click 'Verify'. It should be successful like what's on the screenshot below:
Once you've done all of the steps above, you can now input your 3rd-party domain on your Google Blogger Blog's setting. It will provide you the two CName that you need to apply to the DNS Setting of your Domain Provider (see screenshot below).
Apply the necessary DNS settings to your Domain provider and then you're all done.
Hope this fix helps.
Thanks! :)
