HTTP Push Data Advanced sensor - Why does XML/JSON require "content=" string?

I created HTTP Push Data Advanced sensor with HTTP Request Method = POST I use Postman to test sending the HTTP POST to http://<my_prtg_ip>:5050/<token>

Test 1:

If I use the following POST content, I received error: No response (code: PE002) in PRTG

{
  "prtg": {
    "result": [
      {
        "channel": "MyChannel",
        "value": "12"
      }
    ],
    "text": "Breaking news 2"
  }
}

Test 2:

If I use the following POST content (notice "content=" in 1st line), PRTG can receive successfully

content=
{
  "prtg": {
    "result": [
      {
        "channel": "MyChannel",
        "value": "12"
      }
    ],
    "text": "Breaking news 2"
  }
}

Test 3:

If I use the following POST content, I received error: No response (code: PE002) in PRTG

{<prtg>
	<result>
		<channel>MyChannel</channel>
		<value>10</value>
	</result>
	<text>Mary%20has%20a%20little%20dove</text>
</prtg>

Test 4:

If I use the following POST content(notice "content=" in 1st line), PRTG can receive successfully

content=
<prtg>
	<result>
		<channel>MyChannel</channel>
		<value>10</value>
	</result>
	<text>Mary%20has%20a%20little%20dove</text>
</prtg>

• Question: Is this a bug?

http-push-data-advanced-sensor json xml