Avoid ESOCKETTIMEDOUT from Google/Firebase Cloud Functions - node.js

Question

I have a Firebase cloud function, that is looping through users in a database and sends an email to each one. It uses the Campaign Monitor API for Transactional/Smart Emails, but the request results in an ESOCKETTIMEDOUT error. Campaign Monitor receives and processes each request just fine, but I would like to avoid the error of course.
How can I do this? I've read elsewhere about a setting, 'agent: false, pool: {maxSockets: 100}', but I am not sure if this is the right approach - and I don't know where to set it on a Firebase og Google Cloud Function.
This is the request snippet, that is called by the loop.
api.transactional.sendSmartEmail(details, function (err, res) {
if (err) {
console.log('error sending mail, err);
/*Throws:
{ Error: ESOCKETTIMEDOUT
at ClientRequest.<anonymous> (/user_code/node_modules/createsend-node/node_modules/request/request.js:813:19)
at ClientRequest.g (events.js:292:16)
at emitNone (events.js:86:13)
at ClientRequest.emit (events.js:185:7)
at TLSSocket.emitTimeout (_http_client.js:630:10)
at TLSSocket.g (events.js:292:16)
at emitNone (events.js:86:13)
at TLSSocket.emit (events.js:185:7)
at TLSSocket.Socket._onTimeout (net.js:338:8)
at ontimeout (timers.js:386:11) code: 'ESOCKETTIMEDOUT', connect: false }
*/
} else {
console.log('sent mail');
}
});