Steps to be followed for Twilio Integration to work for ERPNext voice calling (incoming/outgoing)

1. Ensure that you have installed the App required for this to work on erpnext server:

bench get-app https://github.com/frappe/twilio-integration.git
bench --site site_name install-app twilio_integration

In Twilio

1. You need to create a new project in Twilio account to use communication features like whatsapp, voice calls etc through ERPNext.
2. From your Twilio console you can go to a programmable voice section and get a Twilio number to use for calls(make sure that the number is voice capable).
3. Create a TwiML App by passing voice request url as <your_site>/api/method/twilio_integration.twilio_integration.api.voice . Use ngrok to get public domain for your project in case it is running locally.
4. For incoming calls to work, you will have to go to Active Number (https://console.twilio.com/us1/develop/phone-numbers/manage/incoming)
5. Select the number you need to use for incoming
6. Select Webhook, TwiML Bin, .... in "Configure with" field under the "Configure" tab
7. Select "Webhook" in "A call comes in" field
8. Set URL > <site_url>/api/method/twilio_integration.twilio_integration.api.twilio_incoming_call_handler

In ERPNext

1. Go to Twilio Settings and put Account SID & Auth Token
2. Go to role permission manager and give yourself access to level 1 (Read + Write) on Twilio settings doctype, because you will find some fields hidden on the doctype
3. Put the TwiMLSID
4. Enable the Settings and Save
5. Setup Voice call settings for all the people you want to enable the call feature for.
6. Setup Communication medium for allowed calling schedule