Since switching to php 7.1 I've been seeing paypal error 77 when attempting to checkout with paypal. I haven't been able to figure out exactly what the error code represents. I'm using zen cart 1.55f. Any thoughts?

Full Error:
Code:
An error occurred when we tried to contact the payment processor. Please try again, select an alternate payment method, or contact the store owner for assistance. () - (77)