iron-ajax not support content-type='application/json' for POST request

Question

I am trying to use iron-ajax but the content-type='application/json' is not supporting.

<iron-ajax id="ajaxRequestOtp"
                               method="POST"
                               url="[[apiEndPoint]]/user-sms-auth"
                               body="{{requestOtpBody}}"
                               handle-as="json"
                               headers='{"Accept": "application/json"}'
                               on-response="_responseRequestOtp"
                               on-error="_errorResponseRequestOtp"
                               content-type='application/json'>
                    </iron-ajax>

Property -

static get properties() {
            return {
                apiEndPoint: {
                    type: String,
                    value: 'http://example.com'
                },
                requestOtpBody: {
                    type: String,
                    computed: '_createRequestOtpBody(mobileNumber)',
                    notify: true
                }
            };
        }

Computed function -

_createRequestOtpBody(mobileNumber) {
            let body = {
                phone_number: "+91" + mobileNumber
            }
            return JSON.stringify(body);
        }

This is not working, 404 Bad request. I need to send a JSON object to my server.

Error Message-

OPTIONS http://example.com/user-sms-auth 404 (Not Found)
(index):1 Failed to load http://example.com/user-sms-auth: Response for preflight has invalid HTTP status code 404

Answer 1

Make requestOtpBody => type: Object, and skip the JSON.stringify step.

_createRequestOtpBody(mobileNumber) {
    return { phone_number: "+91" + mobileNumber };
}