Create a HTTP POST to Twilio Functions (send SMS) - twilio

Question

I have created a Twilio function that I would like to use to send my affiliate referral link to subscribers of an application that come through my channel.
It works fine with a static to / from number, however I would like to make the "to" field a dynamic variable that can be manipulated via a HTTP/Webhook POST when a Zapier detects a new subscriber to my Mailchimp mailing list and pass their phone number as the variable.
I am also unclear what I need to do to authenticate the client (Zapier) that is making the POST as I do not want the function open to the world to use, if any insights can be shared on this it would be sincerely appreciated - I am a very inexperienced programmer trying to learn very quickly!
#philnash - thanks for your suggestion, implementing it slowly!
Many thanks in advance!
exports.handler = function(context, event, callback) {
const appCodes = ['code1', 'code2', 'code3', 'code4']
var smsBody = refCode ();
function refCode () {
return appCodes[Math.floor((Math.random() * appCodes.length))];
};
context.getTwilioClient().messages.create({
to: '[phone]', // How do I make this dynamic from HTTP/Zapier Webhook POST???
from: '[phone]',
body: `Get the App: ${smsBody}`
}).then(msg => {
callback(null, msg.sid);
}).catch(err => callback(err));
}

Answer 1

Twilio developer evangelist here.
I presume the Zapier webhook is sending the details, including the phone number, as the body of the POST request.
All the parameters in a request body appear on the event object that is passed into your handler. You probably want to run a test where you print out the contents of the event object to see what you are being passed. You can do this with:
exports.handler = function(context, event, callback) {
for (let key in event) {
console.log(`${key}: ${event[key]}`);
}
// ... rest of the function
}
Then, when you figure out what parameter is storing the number, you can use that in the call to create the message.
Let me know if that helps at all.

Answer 2

Try this:
exports.handler = function(context, event, callback) {
for (let key in event) {
console.log(`${key}: ${event[key]}`);
}
// ... rest of the function
callback(null, 'complete');
};

Answer 3

Thanks everyone for your input, it was sincerely appreciated! I was able to solve this with the following code:
exports.handler = function(context, event, callback) {
const appCodes = ['code1', 'code2', 'code3', 'code4']
var smsBody = refCode ();
var subNum = event.primaryPhone || 'There is no subscriber number'; // primaryPhone sent via HTTP post to twilio function
function refCode () {
return appCodes[Math.floor((Math.random() * appCodes.length))];
};
context.getTwilioClient().messages.create({
to: `${subNum}`, // parameters & values recieved from HTTP POST are available within the twilio functions "event" context
from: '[phone]',
body: `Get the App: ${smsBody}`
}).then(msg => {
callback(null, msg.sid);
}).catch(err => callback(err));
}