API 401 Error Code

My GET request is claiming to be unauthorized. Please help me figure this out!

    useEffect(() => {
        //Fetching an API (data)
        fetch('https://us.api.blizzard.com/data/wow/mount/index?namespace=static-us&locale=en_US&access_token=MYTOKEN')
        //Converting that data into readable json
        .then(response =>  response.json())
        //Setting the state to the user data that is returned by the API
        .then(mounts => {
            setMounts(mounts.mounts)
        })
    }, [])

This has been working for the last 2 days and randomly stopped today so I am very confused. It is throwing a 401 error code at me and I am unsure why?

Your token expired. It’s valid for only 24 hours after the last time you sent your client id/secret to the /oauth/token endpoint.