Why are PayPal card payments being declined on my website?

[Focus_Scotland]

Hi all. I've had a Shopify site since 2011, have been processing all my card payments via PayPal for the last 5 or 6 years but suddenly it's stopped working. Customers payments being declined apparently due to 3D Secure issues. 

I was informed by a PayPal representative on the phone yesterday that there is now no way to accept card payments using PayPal's processing methods on a shopify website. Which I'm finding very hard to believe. 

Could anyone offer any advice as to what the issue with declined payments might be and if the PayPal rep was correct or not? 

Many thanks.