JavaScript - How to Send Mixed Content Type in an Ajax Post?

This is similar to a previous post I made but I'm still confused and need help. I have two pieces of data to send to a service. I need to send, using javascript, an "action" which is JSON and I need to send a "submittingURL" which is just the encoded URL. Is there a way to send both pieces of data in the POST? If so how? This is all new to me. Below is the same function sending both as a GET and then the second one splits it so the JSON is POSTed. How can I send both via POST even though mixed content types (no jQuery)?

function sendUnapprovedAction(action) {
    var req = new XMLHttpRequest();
    var url = '//001l60fbadm:10001/marketingcampaigns/api/v1/campaigns?action=' +
    encodeURIComponent(JSON.stringify(action)) + '&submittingURL=' + 
    encodeURIComponent(_satellite.getVar("Full URL"));
    req.open('POST', url, true);
    req.setRequestHeader('Content-Type', 'application/json');
    req.send();
};

function sendUnapprovedAction(action) {
    var req = new XMLHttpRequest();
    var url = '//001l60fbadm:10001/marketingcampaigns/api/v1/campaigns?submittingURL=' +
    encodeURIComponent(_satellite.getVar("Full URL"));
    req.open('POST', url, true);
    req.setRequestHeader('Content-Type', 'application/json');
    req.send('action=' + encodeURIComponent(JSON.stringify(action)));
};`

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Thanks!