You can make an outbound call using below API with the help of a REST Client
The auth_id can be procured from your dashboard https://manage.plivo.com/dashboard/
There are three mandatory requirements that must be met to make an outbound call
The phone number to be used as the caller id (with the country code).For Example, a USA caller id number could be, 15677654321, where '1' is the country code.
Use the regular number(s) or sip endpoint(s) to make a call.
Regular number must be prefixed with country code but without the + sign. For example, to dial a number in the USA, the number could be, 15677654321, where '1' for the country code.
Sip endpoints must be prefixed with sip:
Example, sip: firstname.lastname@example.org.
The URL invoked by Plivo when the outbound call is answered.
To add additional options on the API, please refer https://www.plivo.com/docs/api/call/#arguments