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Make sure you have enabled Custom DevState hints. Log into your PBX GUI and navigate to the Advanced Settings module:
In the top menu go to Settings
In the drop-down menu go to Advanced Settings
At the top, under the Advanced Settings Details section, set Display Readonly Settings and Override Readonly Settings to "Yes":
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Message Bar on screen not updating when changing items like DND or Follow Me
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Log into your PBX Admin GUI and navigate to the to Sysadmin module.
In the top menu go to Admin
In the drop-down menu go to System Admin
Select the Port Management section in the navigation menu.
Look to see what port Restful Phone Apps are using.
Open a Web Browser and go to the following URL: http://IPADDR:PORT/applications.php/donotdisturb/main?user=EXT#
Replace IPADDR with the IP Address of the PBX.
Replace PORT with the port number Restful Phone Apps are using as defined in Sysadmin Port Management.
Replace EXT# with your extension number.
This should bring up some XML such as:
{"application_name":"donotdisturb","application_display":"DND","page_name":"main","type":"display","exitPath":null,"layout":[{"type":"bool","name":"status","display":"Enabled","value":false}],"action":[],"error":[]}
If you get nothing returned, this means your port is either not opened on your firewall or not defined correctly. Try and resubmit the Port Management page in Sysadmin by pressing the Submit and Apply Config buttons.