RCP Member Discount getting doubled when checking out with PayPal

[dgoldak]

Original issue but determined to be related to PayPal: https://github.com/easydigitaldownloads/edd-rcp-member-discounts/issues/14

Bug Report

Expected behavior

When a RCP member discount is applied, checkout using PayPal should charge the expected total.

Actual behavior

PayPal either changed the wrong amount or we get error:
Things don't appear to be working at the moment. Please try again later.

1. What appears to be happening is the discount is getting doubled. Therefore the error is caused by the error being $0. You can confirm this by adding an item to cart that isn't eligible for RCP discount.
2. If the incorrect total is $1 or more, PayPal Pro will process the payment but at the wrong price. PayPal Standard will fail, I assume due to the EDD price not matching the PayPal price.

I'm not able to replicate PayPal Pro myself due to sandbox issues but here is a screenshot from the customer:

In the screenshot, you can see that the Discount in PayPal is wrong, $7 instead of $3.50.

Steps to reproduce the behavior

1. Setup a RCP Member Discount at 50%.
2. Log in as RCP member
3. Add download to cart, member discount should be applied
4. Checkout with PayPal Standard
5. Should be redirected to PayPal to process payment - with no errors.
6. Confirm payment in complete in EDD
7. Confirm PayPal amount & discount is correct
8. Repete steps with PayPal Pro

Information:

PHP Version: 7.1

EDD RCP Member Discounts Version (or branch): master

EDD Version (or branch): master

WordPress Version: 5.0

Any other relevant information: Originally reported by a customer.
https://secure.helpscout.net/conversation/718764724/95475?folderId=1847242

Tested with Stripe which works as expected, this issue appears to be specific to PayPal.

[dgoldak]

@misulicus discovered the following:

Replicated with a standard EDD product of 4.99 and a member discount of 10%
On checkout page price is correct: Purchase Total: $4.49
But once you reach the PayPal page the price goes to $3.99. Discounted for $1 instead of $0.50

Did some debugging in paypal stadard and on these lines is where the discount gets set to $1
https://github.com/easydigitaldownloads/easy-digital-downloads/blob/master/includes/gateways/paypal-standard.php#L296-L301

this is my testing block

       if( $paypal_sum > $purchase_data['price'] ) {
            var_dump( $paypal_args['discount_amount_cart'] );
            $difference = round( $paypal_sum - $purchase_data['price'], 2 );
            var_dump( $difference );
            if( ! isset( $paypal_args['discount_amount_cart'] ) ) {
                $paypal_args['discount_amount_cart'] = 0;
            }
            $paypal_args['discount_amount_cart'] += $difference;
        }
var_dump($paypal_args['discount_amount_cart']);exit;

and that returns string(4) "0.50" float(0.5) float(1)

so $paypal_args['discount_amount_cart'] = "0.50" at the top then $difference = 0.5 and then at the end $paypal_args['discount_amount_cart'] += $difference; adds them so it turns to 1

[cklosowski]

@dgoldak Can you replicate without member discounts but using Discounts Pro or something that adds a negative fee to it?

[dgoldak]

@cklosowski I confirmed Discounts Pro works properly with PayPal:

[dgoldak]

Tested PayPal Express 1.4.4 & master and this issue doesn't appear to be affect Express. Order processes successfully with the correct amount.

[ashleyfae]

Closing this in favour of #6837 . Pretty sure it's the same issue.