checkIfPro.js

checkIfPro(){
  // Send email and PRO_PRODUCT_ID to check.php.
  // check.php must get the list of all users from Paddle, then see if current user is among Pro users.
	const userEmail = "email@example.com";
	const PRODUCT_ID = 11111; //See this ID in the Paddle dashboard.
  const URL = 'https://unicornplatform.com/api/check.php';
	const data = {
        email: userEmail,
        productID: PRODUCT_ID
    };
	const PARAMS = {
        headers: {
            "Accept": "application/json",
            "Content-Type": "application/json; charset=UTF-8"
        },
        body: JSON.stringify(data),
        method: 'POST'
    };
    fetch(URL, params)
        .then(res => res.text())
        .then(response => {
            let res = JSON.parse(response);
            //PHP script returns an object.
            if(res.isPro === 'true'){
                // It's a Pro user.
            }else{
	            // It's a free-plan user.
            }
        })
        .catch(error => console.error('Error:', error));
}