MarketPress checkout not working

Using MarketPress on a multisite, when someone tries to place an order the “Add to Cart” button and the “Checkout” page just spins and never submit.

https://static.livechatinc.com/8801096/P6293KXR44/c21cc6e8dd602eab048604f2ddd01a01/Checkout___THE_HOOP_Basketball_Academy_%F0%9F%94%8A.png