The HTTP header Content-Type is missing or its value is invalid error in REST API in SharePoint 2013/2016/Online

This SharePoint Rest API tutorial explains, how to solve “The HTTP header Content-Type is missing or its value is invalid” error which comes in Rest API in SharePoint 2013.

Recently I am trying to retrieve some information using SharePoint 2013 REST API. I wrote the code like below:

headers: {
"accept": "application/json;odata=verbose",
"X-RequestDigest": $("#__REQUESTDIGEST").val()
}

But it gave me error like:
Microsoft.SharePoint.Cient.ClientServiceException. The HTTP header Content Type is missing or its value is invalid. Unsupported Media Type. The error looks like below:

The HTTP header Content Type is missing or its value is invalid

The error was coming because content-type was missing and it got resolved by adding the below line:

"content-type": "application/json;odata=verbose"

The full code looks like below:

headers: {
"accept": "application/json;odata=verbose",
"content-type": "application/json;odata=verbose",
"X-RequestDigest": $("#__REQUESTDIGEST").val()
}

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Hope this SharePoint tutorial helps to resolve, The HTTP header Content-Type is missing or its value is invalid error in REST API in SharePoint 2013/2016/Online