My Checkout is directing me to a 404 page. Please help!

The checkout link for my store is not adding “/index.php/” to the link and is causing a 404 error. All the other links that I have on Marketpress are working fine until you start the checkout process and that’s where the links are not correct.

The link currently is “”.

Where it should be “” which actually works and continues the checkout process.

I have my permalink settings correctly set to “” as indicated in your walkthrough videos.

Could you please tell me what I need to do in order to straighten this issue out?