error when sending an email via fetch to react

To send an email, I use action which is required to send data via fetch.

And it works by sending mail, but I always get the error:

VM65:1 Uncaught (in promise) 
SyntaxError: Unexpected token '<', "<!DOCTYPE "... is not valid JSON 

I guess the problem is in body:

body: new FormData(Email.current)

What could be the error?

const [EmailUserData, setEmailUserData] = useState({DataOne: '', DataTwo: ''});
const FormEmail = useRef();

const SendEmail = (event) => {
   event.preventDefault()
   fetch("https://submit.jotform.com/submit/XXXXXXXXXXXXX", {
      method: 'POST', 
      body: new FormData(FormEmail.current)
   })
   .then(res => res.json())
   .then(data => {
      console.log(data)
   })
}

<form method="post" ref="{FormEmail}" onSubmit="{SendEmail}">
    <input type="text" name="data_1" onChange={event => setEmailUserData({...EmailUserData, DataOne: event.target.value}) } value={EmailUserData.DataOne || ''} />
    <input type="email" name="data_2" onChange={event => setEmailUserData({...EmailUserData, DataTwo: event.target.value}) } value={EmailUserData.DataTwo || ''} />

    <button type="submit">Submit</button>
</form>