There is an error that is preventing partial payments working in the js script tag code in this file:
wp-invoice/lib/class_template_functions.php
The current code from lines 397-401 is as follows:
my_amount.on("touchleave", function(){
var new_value = my_amount.val();
payment_amount.val( validate_amount( new_value ) );
set_pay_button_value();
}
The above is missing a closing round bracket on the last line, see below:
my_amount.on("touchleave", function(){
var new_value = my_amount.val();
payment_amount.val( validate_amount( new_value ) );
set_pay_button_value();
})
Adding this closing bracket fixes the issue.
I haven’t notified the developers about this issue as they don’t seem to have any way to contact them without requesting a quote for custom work. Hopefully they will pick up on it here.