Prestashop Checkout and PHP 7.2 - Errors at Checkout

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On Prestashop v.1.7.7.2 using Prestashop Checkout v2.12.0 and PHP 7.2

Selecting 'Checkout' on the 'Personal Information' page throws a 404 or 500 error in some browsers (chrome incognito, firefox, mobile browsers) but works fine in other browsers (chrome non-incognito, edge). Paypal payment seems to work fine in all.

Switching PHP to 7.4 fixes the issue. However, Printful API sync does not support PHP 7.4 and must use PHP 7.2

Bit of a complicated issue, any ideas why the add on would work in some browsers but not others? Thanks.