Strange behaviour when using wpinv_get_item_price filter hook. Possible bug?

[aayla-secura]

Not 100% if it's a bug or I'm doing it wrong.

Am I correct that if a developer wants to programmatically and dynamically change how much a user is charged for an item, they should add a filter hook for wpinv_get_item_price? As in:

add_filter(
    'wpinv_get_item_price',
    function ($price, $item) {
        return 50; // or whatever, dynamic based on other conditions
    },
    10,
    2
);

I'm doing this and seeing some strange behaviour.

1. Firstly, when I change the price using this filter hook to 0, to make the item free for some users, checkout fails with a vague error: "An error occured while processing your payment. Please try again." and nothing more is logger either.

2. Secondly, when I change the price to something above 0, even though the user is charged the custom amount I return from the filter hook, at least according to Stripe, the total amount of the invoice reflects the original price, which is confusing:

3. The third peculiarity, is that when I return a custom price from that filter hook, the user-set/dynamic pricing during checkout no longer works. The price that the user inputs always gets overridden with what I return from the hook. If I just return the original price from the hook, it works again...

---

What is the correct way to set dynamic pricing server-side (i.e. not using "let customer name their price")? And how is the wpinv_get_item_price supposed to be used?

[aayla-secura]

Well, I found a way to set an item price during checkout: using the filter hook getpaid_payment_form_submission_processed_item and editing the form item's price there works as expected.

But I'll leave this open as I wonder whether the wpinv_get_item_price should also have the same effect, or if not, what is its intended use case?