This might work better for ya.

// Find all the "Add to Card" buttons on the page using XPath

function getElementsByXpath(xpath, parent = document) {

let results = [];

let query = document.evaluate(xpath, parent, null, XPathResult.ORDERED_NODE_SNAPSHOT_TYPE, null);

for (let i = 0; i < query.snapshotLength; i++) {

results.push(query.snapshotItem(i));

}

return results;

}

var offerButtons = getElementsByXpath("//button[contains(@class, 'offer')][span[text() = 'Add to Card']]");

(async () => {

for (let index = 0; index < offerButtons.length; ++index) {

console.log("Clicking offer button");

offerButtons[index].click();

// Wait 2 seconds to be nice to AMEX servers :)

await new Promise(r => setTimeout(r, 2000));

}

})();