Customers cant get to Confirmation page when finalizing a purchase, results only in a HTTP 500 error

Hi Open Cart community,
I am a developer helping a customer to fix an error on his Open Cart website.
The customers version of Open Cart is 2.0.1.1, and using Ajax Quick Checkout Version 6.4.1. Using PHP 7.2 on the webhost.

The error is that whenever a customer clicks the confirm button when in checkout, nothing happen for the customer. But when using inspect on webpage, there are a HTTP 500 error in the console.
Looking more into the error logs of the webpage in the FTP(specificly in the twe.php file) a error text reads as following "Use of undefined constant positions - assumed 'positions'". Then following this error leads me to this line of php code: Where it is trying to build a array of postions and directing it to the place in the file structure, have been looking for it in FTP, but cant find common/positions anywhere.
Also this piece of code is used in many files.

Hope that anyone has a guess or even encountered this error before and maybe solved it, any hints or educated guess is welcome. Also if there is a soloution, please share.

Kind regards
Jesper Engdahl

Hello Jesper,

it sounds really weird if a developer asks here for help.
While this bug or error should be a common task for an exerienced dev.

An extensions is getting some stored values from the database and assign it to new variables.
You should now find which extension is that, I assume the Qucik Checkout is the Eval.

Basically you should ask for support at the developer of that extensions, rather asking here for help.
Because - I assume again - that this extension is a paid one, therefore you have the right for support.