Hello! I have the same issue. ??
I get the CANNOT BE ZERO OR NEGATIVE error when using my PayPal plugin. When I use the standard PayPal option built in, I get the Session Expired email.
I have narrowed it down to whether or not you are logged in prior to trying to press the Proceed to Payment button.
If I’m logged in, it lets me get to PayPal… if I’m not logged in, the session expires.
I’ve tried switching payment methods only to get the ZERO/NEGATIVE error listed above.
Thanks!
-Drew