0 call to undefined function mcrypt_encrypt()

-- HikaShop version -- : 4.3.0
-- Joomla version -- : 3.9.8
-- Browser(s) name and version -- : chrome
-- Error-message(debug-mod must be tuned on) -- : 0 call to undefined function mcrypt_encrypt()

Hello,

When people go to the checkout and select the credit card payment option and hit the payment button, they get an error page with this text: 0 call to undefined function mcrypt_encrypt(). I really have no idea what it is. Can you solve my problem?

Problem solved by putting PHP back to PHP7.1. where the module is still active.

Best regards,

Nico