Status code 400 in Events API V2

Hi,
I’m new to PagerDuty.
I’m trying to send (trigger) an event via Events API V2 using JavaScript layer from another application (Ivanti).
I keep getting status code 400 error
(Bad request) with {ā€œerrorsā€:["ā€˜payload’ is missing or blank"],ā€œmessageā€:ā€œEvent object is invalidā€,ā€œstatusā€:ā€œinvalid eventā€}

I don’t know what is wrong. I tried changing the payload in several ways to no avail.
Details of the call:
(…)
var JSONimport = {Payload: {summary: ā€œTest eventā€, source: ā€œIvantiā€, severity: ā€œcriticalā€}, routing_key: ā€œrouting_key_hereā€, event_action: ā€œtriggerā€};

var data = JSON.stringify(JSONimport);

var request = ExecuteWebRequest(ā€˜POST’, ā€˜https://events.eu.pagerduty.com/v2/enqueue’, data, {Headers: {ā€œContent-Typeā€:ā€œapplication/jsonā€, ā€œAuthorizationā€:ā€œToken token=<api_token_here>ā€}, SkipServerCertificateValidation: false});

[Note: ExecuteWebRequest is just a ready javascript method in Ivanti Web Services layer.]

Thanks for any suggestion.
Cheers,
Rinaldo