Trying to find out why my POST method isn't being sent to the PHP server in my async request

Question

Whenever I try the request I'm finding that the information isn't being sent to the server. I checked the network in inspection and I'm receiving a status of 200, but for some reason it just won't recognize the post is set. Any help would be massively appreciated

Here's my javascript

    const getLocationInfo = async (lat, lng) => {
        const payload = {
            coordinateData: coordinateData
        };
        console.log(JSON.stringify(payload))

        try{
            const response = await fetch(url, {
                method: 'POST',
                headers: {
                    'Content-Type': 'application/json'
                },
                body: JSON.stringify(payload)
            
            });

            if(response.ok){
                const responseData = await response.json()
                console.log(responseData)
            } else {
                const errorResponse = await response.text();
                console.error('Error:', response.status, errorResponse)
            }
        } catch(error){
            console.error('Error:', error)
        }



    }

    getLocationInfo(100, 100)

And here's the beginning of the PHP code that. Only the beginning is significant because it always just defaults to the "else" statement

     if (isset($_POST['coordinateData'])) {
     ////all the code that is skipped

Thank you for any advice or pointers you can give. I've spent the last 8 hours googling and searching for any errors in my code and tried many different things.