Can anyone reveal the secret to accessing the caller ID (Customer Number) in Vapi to capture field value and use for appointment booking? Tried everything and all I can get is the field to show the name either Customer_Number or {{Customer_Number}} to appear as the value. See the number in the log coming from Twillio but just can't get the actual value.

Extract the phone number from Twilio or headers and pass it into assistantOverrides.variableValues and customer.number when initializing the call, then reference it using {{callerId}} or {{customer.number}} in your prompt to use it for appointment booking..