Payments Won't Process

[strugglingnovice]

I had a customer contact me this morning that they couldn't check out in the shopping cart. I tried, using a credit card and PayPal, using a credit card I get the following:
Please select a payment method for your order.
Error The credit card number starting with was not entered correctly, or we do not accept that kind of card. Please try again or use another credit card.
Error The credit card number starting with was not entered correctly, or we do not accept that kind of card. Please try again or use another credit card.

When I try using PayPal, nothing happens.

I'm running version 5.5f -I haven't updated because I don't know how to do this and haven't had problems until now.

Hopefully there is a fix for this without having to go to a newer version of ZenCart, it would be really difficult for me to accomplish this. I use authorize.net to process payments.

Thanks for any help you can give me, I appreciate it.

[lat9]

I had a customer contact me this morning that they couldn't check out in the shopping cart. I tried, using a credit card and PayPal, using a credit card I get the following:
Please select a payment method for your order.
Error The credit card number starting with was not entered correctly, or we do not accept that kind of card. Please try again or use another credit card.
Error The credit card number starting with was not entered correctly, or we do not accept that kind of card. Please try again or use another credit card.

When I try using PayPal, nothing happens.

I'm running version 5.5f -I haven't updated because I don't know how to do this and haven't had problems until now.

Hopefully there is a fix for this without having to go to a newer version of ZenCart, it would be really difficult for me to accomplish this. I use authorize.net to process payments.

Thanks for any help you can give me, I appreciate it.

You're right, zc155f was released on December 31, 2017 ... in programming-time, when dinosaurs roamed the earth!

Did your webhost silently update the version of PHP on which the site runs? That's happening more and more as older PHP versions are no longer supported. Note that zc155f was designed to run on PHP 5.5 through 7.1.

Are there any myDEBUG*.log files present in the site's /logs sub-directory?