1. Create a new trunk in Skip2PBX:

Open your Skip2PBX web interface and go in Channels > SIP > SIP trunks and create a new trunk:

Authentication mode	Username and password
Link mode	Single user
Username	xlite
Password	xlite
Auth username	xlite
DTMF Mode	INFO

2. Create a new account in your X-LITE:

Go to SIP Account Settings > Add... and fill in the following values:

Display Name	Your name
User name	xlite
Password	xlite
Authorization Username	xlite
Auth username	xlite
Domain	Your Skip2PBX IP