Office.context.mailbox.item.body.getAsync returns error 9020 An internal error has occured

Question

I am using a tutorial that gets the email email properties using Outlook Add-in and now I am trying to get the email body. All the research I am getting is using mostly this statement to get it.

function getEmailBody() {
  Office.context.mailbox.item.body.getAsync(Office.CoercionType.Text, function callback(asyncResult) {
       return asyncResult.value;
});

But when I run it, it returns empty and when I put a debugger on it, the asyncResult has these values:

value: null
status: failed
error: OSF.DDA.Error
  name: GenericResponseError
  message: An internal error has occurred.
  code: 9020

Does anyone knows what is causing this error? I am using outlook.office.com in Google Chrome to access the emails.