How to resolve 407 Proxy Authentication

407 Proxy Authentication SIP message is a normal authentication challenge. It is sent from Service Provider to challenge the endpoints.

Upon receiving 407 Proxy Authentication, the endpoint sends the second INVITE including the credentials.

To solve this in Grandstream IP Phones, please go to the phone's Web GUI => ACCOUNT => SIP settings => Custom SIP headers => set "No" to all of these options:

• Use Privacy Header

• Use P-Preferred-Identity Header

• Use X-Grandstream-PBX Header

• Use P-Access-Network-Info Header

• Use P-Emergency-Info Header

• Use MAC Header