I had a few people test this and no one had issues. So try this:
1. Go to Settings, scroll down and tap on Safari
2. Make sure Accept Cookies is set to either "From visited" or "Always"
3. Make sure JavaScript is On
Warning: the following step will delete your browsing history. Do not proceed if you wish to keep it.
4. Tap "Clear History" and "Clear Cookies and Data"
5. Open Safari, head to rui-products.com and try placing the order again