Few things, it can take up to 10 minutes for a new number to be registered, so if you added the phone number to a group and tried immediately for Phone Verification, there is a chance that the number was not setup yet.
Second common issue websites will only wait a certain amount of time to connect, if there is an extended pause during the line forwarding, the website c may hang-up. To get an instant connection, what I recommend is changing your setting from forward to Voicemail. In the voicemail option, the connection occurs immediately. The website will be able to leave your pin code on a voicemail message. That message will be available to be played from our reporting section in Linespan and will be forwarded to your email address as a .WAV file. This should solve your problem.
Next, be sure you associated the number with a group on Linespan.