Order is not created after returning from payment through PayPal

Hello,
Zen Cart version: v1.3.9e
This is the first version I installed, no upgrades

I have a website through which I sell products and I use PayPal as my only payment method.
I never had any problem like this before. I only noticed it yesterday with the last customer.
Problem Description:
Account created OK
Products added to the cart OK
Going to checkout and choosing PayPal (only option) OK
Completing payment OK
Returning to my website - does not create a new order, no confirmation, product is not marked as out of stock - as if nothing happened.

The only way I knew products have been purchased and payed for was that a new account was created and PayPal sent me a notification about a payment that has been made.

I tested with a test customer - same thing payment completes but no evidence that an order has been made.
I also imported the Database installed it on my computer and tested the whole thing with XAMPP - same results.

My store has been active for a long time this is the first time it happens.

Please help,
Thanks,
Amnon.
email: [email protected]

Paypal IPN or Express ? If IPN, remove it and install Express, which is much more reliable.

Thanks. What does Express do? Does it require special settings in my PayPal account? Can any customer use it to pay?

It looks like PayPal has changed something in their code that results in a bug in this version of Zen Cart

The old module you're using relies on waiting for PayPal's servers to send what's called an "IPN" to your server to tell your store about the payment that has been made. And then your server needs to talk to PayPal's server to verify the data it receives. ALL KINDS OF THINGS can go wrong in that process, including your own server's configuration might have been changed recently to disallow those incoming or outgoing communications. Or something might be wrong in your Paypal account which has shut off the IPN notifications from being sent to you.
Plus a myriad of other potential issues.
That's just the way the technology PayPal uses for that approach works.

The Express Checkout method talks directly with the PayPal server to confirm payment information while the customer is present, and thus your store knows immediately that the order has been placed. As such it's far more reliable, and uses far more modern methods of doing what it needs to do.

Setup is easy: https://www.zen-cart.com/getpaypal

You really ought to upgrade to the latest version of Zen Cart to benefit from fixes of known bugs.

And, yes, EC can be used by anybody to make payment. PayPal's normal limitations apply to both approaches.
https://www.zen-cart.com/tutorials/index.php?article=28

Thank you very much!
I will switch to express and see if it fix the problem.