Why my Digium SIP trunk is stuck in authenticating status

This issue can also be described as Switchvox showing authenticating in the conection status, Failed to autenticate a SIP peer in asterisk or in general description of the problem, sip.digiumcloud.net keep challenging (401) SIP registrations request. 
 

Packet capture  example that shows an system with this issue. Please note that every REGISTER attempt is responded by a 401 by sip.digiumcloud.net 

The problem is caused by user using a wrong password, most likely there is either a space at the beginning or end. Please ask the customer to reconfigure the account or if they have recently requested a password change.