Custom Woocommerce checkout filed yields a Json error when validating [closed]

I figured this out. What fixed it was I needed to use isset in the conditional.

old code:

if (!$_POST['delivery']){
    wc_add_notice( sprintf(__('You must accept Additional Shipping Conditions.', 'themename')) ,'error'  );
} 

if (!$_POST['customer']){
    wc_add_notice( sprintf(__('You must accept responsibility for address misplacement.', 'themename')) ,'error'  );
}

Correct code using isset:

if (!isset($_POST['delivery'])){
    wc_add_notice( sprintf(__('You must accept Additional Shipping Conditions.', 'themename')) ,'error'  );
} 

if (!isset($_POST['customer'])){
    wc_add_notice( sprintf(__('You must accept responsibility for address misplacement.', 'themename')) ,'error'  );
}