From PayPal payment it goes back to Cart page

I think I'm pulling my hair on this one. My store just loops between PayPal and the cart. Any suggestions?

https://www.massiveintent.com/shop

To give you some background I used to have it setup under LinkPoint and now I'm changing it to PayPal. Thought it would be easy but it hasn't been. Need help asap please!! :)

Click Reply below and answer the questions in the "Posting Tips" section.
And also indicate which paypal module you're using. And if it's not Express Checkout, please explain why.

Zen Cart 1.3.8a

I used to have it setup under LinkPoint and now I changed it to PayPal.

I have all three PayPal options on.

https://www.massiveintent.com/shop

Well, Website Payments Pro is a subscribed service, so unless you've paid for that you'll want to click Remove on that one.

And, since Website Payments Standard (IPN) is the old method that's less reliable, it's better to click "Remove" on that one too, and just use Express Checkout.

Also, since v1.3.8a has some known security vulnerabilities, it's STRONGLY recommended that you upgrade to v1.3.9.

Is the upgrade simple or would I basically start from scratch again?

Also, is there anywhere that offers paid support? I really need this fixed asap and the person who originally set it up won't be available for weeks.

The upgrade is only as complex as the customizations you've made to the site.
Upgrade instructions here: https://www.zen-cart.com/tutorials/index.php?article=98

As for paid help, there's a Commercial Help Wanted section of the forum where you can post requests for paid assistance and entertain quotes from people interested in doing that kind of work. You must vet them yourself though.