One-Page Checkout [Support Thread]

v2.6.1 of One-Page Checkout is now available for download: https://www.zen-cart.com/downloads.php?do=file&id=2095

This release contains changes for these GitHub issues:

#462: Ensure $_POST['order_id'] is an int.
#461: Fix event-handler duplication on checkout_one page

opc v2.6.1, zc2.1.0, paypalwpp, php 8.1

I received the following intermittent warning.

[11-May-2026 15:08:12 America/New_York] PHP Fatal error: Uncaught Error: Typed property OnePageCheckout::$isVirtualOrder must not be accessed before initialization in /includes/classes/OnePageCheckout.php:2568
Stack trace:
#0 /includes/classes/observers/class.checkout_one_observer.php(685): OnePageCheckout->getTaxLocations()
#1 /includes/classes/traits/NotifierManager.php(106): checkout_one_observer->update(Object(notifier), 'ZEN_GET_TAX_LOC...', Array, false, NULL, NULL, NULL, NULL, NULL, NULL, NULL)
#2 /includes/functions/functions_taxes.php(355): base->notify('ZEN_GET_TAX_LOC...', Array, false)
#3 /includes/modules/order_total/ot_tax.php(66): zen_get_tax_locations()
#4 /includes/classes/order_total.php(229): ot_tax->process()
#5 /includes/modules/payment/paypalwpp.php(1637): order_total->pre_confirmation_check()
#6 /ipn_main_handler.php(81): paypalwpp->ec_step1()
#7 {main}
thrown in /includes/classes/OnePageCheckout.php on line 2568

[11-May-2026 15:08:12 America/New_York] Request URI: /ipn_main_handler.php?type=ec, IP address: xxx
--> PHP Fatal error: Uncaught Error: Typed property OnePageCheckout::$isVirtualOrder must not be accessed before initialization in /includes/classes/OnePageCheckout.php:2568
Stack trace:
#0 /includes/classes/observers/class.checkout_one_observer.php(685): OnePageCheckout->getTaxLocations()
#1 /includes/classes/traits/NotifierManager.php(106): checkout_one_observer->update(Object(notifier), 'ZEN_GET_TAX_LOC...', Array, false, NULL, NULL, NULL, NULL, NULL, NULL, NULL)
#2 /includes/functions/functions_taxes.php(355): base->notify('ZEN_GET_TAX_LOC...', Array, false)
#3 /includes/modules/order_total/ot_tax.php(66): zen_get_tax_locations()
#4 /includes/classes/order_total.php(229): ot_tax->process()
#5 /includes/modules/payment/paypalwpp.php(1637): order_total->pre_confirmation_check()
#6 /ipn_main_handler.php(81): paypalwpp->ec_step1()
#7 {main}
thrown in /includes/classes/OnePageCheckout.php on line 2568.

Line 2568 is the following

"if ($this->isVirtualOrder === true || $this->getShippingBilling() === true) {"

The customer under this IP address has placed the order successfully (no sales tax was charged, which is also correct.) and he didn't order the virtual item.

Sigh, that's paypalwpp's "special checkout" mode coming in through the ipn_main_handler.php.

See this OPC GitHub issue with the correction: https://github.com/lat9/one_page_checkout/issues/463

Thanks for your quick fix! I will try and let you know.

Sorry, one more warning. We received an order using paypalwpp. The delivery address somehow was blank (hopefully only intermitent). We also received the following warning from OPC.

[12-May-2026 10:59:16 America/New_York] PHP Fatal error: Uncaught Error: Undefined constant "EMAIL_GREET_NONE" in /includes/modules/checkout_one_send_welcome_email.php:22
Stack trace:
#0 /includes/modules/pages/checkout_success/header_php_guest.php(43): require()
#1 /index.php(35): require('/home/...')
#2 {main}
thrown in /includes/modules/checkout_one_send_welcome_email.php on line 22

[12-May-2026 10:59:16 America/New_York] Request URI: /index.php?main_page=checkout_success&action=create_account, IP address: xxxx
--> PHP Fatal error: Uncaught Error: Undefined constant "EMAIL_GREET_NONE" in /includes/modules/checkout_one_send_welcome_email.php:22
Stack trace:
#0 /includes/modules/pages/checkout_success/header_php_guest.php(43): require()
#1 /index.php(35): require('/home/...')
#2 {main}
thrown in /includes/modules/checkout_one_send_welcome_email.php on line 22.

Line 22 is the following

$email_text = sprintf(EMAIL_GREET_NONE, $firstname);

Update. It seems to be not related to paypalwpp. We received another normal order using paypaldp. It shows the delivery address as normal, but I receive the same warning.

njcyx:

Sorry, one more warning. We received an order using paypalwpp. The delivery address somehow was blank (hopefully only intermitent). We also received the following warning from OPC.

[12-May-2026 10:59:16 America/New_York] PHP Fatal error: Uncaught Error: Undefined constant "EMAIL_GREET_NONE" in /includes/modules/checkout_one_send_welcome_email.php:22
Stack trace:
#0 /includes/modules/pages/checkout_success/header_php_guest.php(43): require()
#1 /index.php(35): require('/home/...')
#2 {main}
thrown in /includes/modules/checkout_one_send_welcome_email.php on line 22

[12-May-2026 10:59:16 America/New_York] Request URI: /index.php?main_page=checkout_success&action=create_account, IP address: xxxx
--> PHP Fatal error: Uncaught Error: Undefined constant "EMAIL_GREET_NONE" in /includes/modules/checkout_one_send_welcome_email.php:22
Stack trace:
#0 /includes/modules/pages/checkout_success/header_php_guest.php(43): require()
#1 /index.php(35): require('/home/...')
#2 {main}
thrown in /includes/modules/checkout_one_send_welcome_email.php on line 22.

> 
> Line 22 is the following
> 
> $email_text = sprintf(EMAIL_GREET_NONE, $firstname);
> 
> Update. It seems to be not related to paypalwpp. We received another normal order using paypaldp. It shows the delivery address as normal, but I receive the same warning.
It's "my bad" in v2.6.1.  The create_account_send_email (and the associated constants' loading) was introduced in Zen Cart 2.2.x and you're using 2.1.0.

That "undefined constant" error has been noted and corrected via this GitHub issue: https://github.com/lat9/one_page_checkout/issues/464

Thanks as always.

I have one more question. Regarding this file in OPC 2.6.1 \includes\templates\template_default\templates\tpl_order_status_default.php, it is the same stock file from zen cart 2.2.2/2.2.1. Can we use it for the early zen carts such as my zen cart 2.1.0?

njcyx:

Thanks as always.

I have one more question. Regarding this file in OPC 2.6.1 \includes\templates\template_default\templates\tpl_order_status_default.php, it is the same stock file from zen cart 2.2.2/2.2.1. Can we use it for the early zen carts such as my zen cart 2.1.0?
Using for zc210 should be just fine, but make sure that you're using the version of /includes/modules/pages/order_status/header_php.php that ships with OPC v2.6.1.

Ok, thanks.

Sorry, it's me again. OPC 2.6.1

I just tried the paypal express checkout button (paypalwpp) in my shopping cart page. After I entered my paypal info and redirect back to my site, I'm under the OPC one page checkout page. I checked the OPC log file. In the last line, it is said "OnePageCheckout: PayPal Express Checkout, in special checkout. One Page Checkout is disabled.'. But it is not disabled. I downgraded my OPC back to 2.5.5 and it is working normal now.

I don't remember if there is a setting under the admin/OPC which I can choose to disable OPC for paypal express checkout or not, but I cannot find it neither 2.5.5 or 2.6.1

Meanwhile, when I saw the OPC one page checkout page (OPC 2.6.1) using paypal express checkout, on the top of the page, it shows a warning: cannot find language file paypalwpp.php. I'm not sure why it shows paypalwpp.php instead of lang.paypalwpp.php. Anyway, I copied lang.paypalwpp.php to paypalwpp.php, but warning remains.

njcyx:

Sorry, it's me again. OPC 2.6.1

I just tried the paypal express checkout button (paypalwpp) in my shopping cart page. After I entered my paypal info and redirect back to my site, I'm under the OPC one page checkout page. I checked the OPC log file. In the last line, it is said "OnePageCheckout: PayPal Express Checkout, in special checkout. One Page Checkout is disabled.'. But it is not disabled. I downgraded my OPC back to 2.5.5 and it is working normal now.

I don't remember if there is a setting under the admin/OPC which I can choose to disable OPC for paypal express checkout or not, but I cannot find it neither 2.5.5 or 2.6.1

Meanwhile, when I saw the OPC one page checkout page (OPC 2.6.1) using paypal express checkout, on the top of the page, it shows a warning: cannot find language file paypalwpp.php. I'm not sure why it shows paypalwpp.php instead of lang.paypalwpp.php. Anyway, I copied lang.paypalwpp.php to paypalwpp.php, but warning remains.
I'll have to play with that a bit, since I don't have any clients (or test credentials) for paypalwpp anymore. I will review the code in the morning and get back with you.

OPC 2.6.0, ZC 2.2.2, free download. Freecharger is enabled. When I try to checkout with OPC, it just spins. When I look at the browser console, it shows a 500 error after a white page. No logs.

swguy:

OPC 2.6.0, ZC 2.2.2, free download. Freecharger is enabled. When I try to checkout with OPC, it just spins. When I look at the browser console, it shows a 500 error after a white page. No logs.
You didn't state whether this was guest or account-holder, but I can't replicate.

I used the demo product's "Single Download" (products_id = 197), changed its price to 0, added to the cart, logged in and went to checkout. No issue.

It was an account-holder. Let me see if I can gather more info. Thanks for trying to repro.

I think the issue is that when the order was originally placed, the download didn't exist. It was fixed after the order was placed.

hmm... nope that wasn't it either. Possibly something weird on the hoster side.

lat9:

I'll have to play with that a bit, since I don't have any clients (or test credentials) for paypalwpp anymore. I will review the code in the morning and get back with you.
That was a long morning! Anyway, here's a commit to OPC's GitHub that corrects the issue where OPC isn't being disabled when in paypalwpp's "special checkout" (i.e. order to be paid via the "Express Checkout" button): https://github.com/lat9/one_page_checkout/commit/b060b03a4d494aafcd6c81af8a0e277cc3c4306a

lat9:

That was a long morning! Anyway, here's a commit to OPC's GitHub that corrects the issue where OPC isn't being disabled when in paypalwpp's "special checkout" (i.e. order to be paid via the "Express Checkout" button): https://github.com/lat9/one_page_checkout/commit/b060b03a4d494aafcd6c81af8a0e277cc3c4306a

Thank you so much!

v4.6.2 of One-Page Checkout is now available for download: https://www.zen-cart.com/downloads.php?do=file&id=2095

This release contains changes associated with these GitHub issues:

#463: Correct PHP fatal error during paypalwpp special checkout.
#464: Correct "undefined constant" PHP error when guest converts to full account on Zen Cart versions prior to v2.2.2.
#465: Correct OPC disable during paypalwpp special checkout.
#466: Correct missing $gender for account registration, if not enabled via configuration.
#467: Use zc300's zen_config when checking configuration settings.
#468: Remove no-longer-needed one_page_checkout_functions.php.