PayPal does not consider +5.00 to be the same as 5.00. Remove the sign from the number. Fixes bug #12152.

docs/changelog/7.x.x.txt

@@ -8,6 +8,7 @@
  - fixed #12139: break on calander feeds during upgrade
  - fixed #12136: Unable to add more than one image in Story
  - fixed #12133: RenderThingData macro doesn't accept templateId
+ - fixed #12152: PayPal Standard ignores shop-credit
 
 7.10.17
  - fixed: Forced to use a PayDriver even with a balance of 0 in the cart.

docs/gotcha.txt

@@ -7,6 +7,12 @@ upgrading from one version to the next, or even between multiple
 versions. Be sure to heed the warnings contained herein as they will
 save you many hours of grief.
 
+7.10.17
+--------------------------------------------------------------------
+    * Due to a formatting problem with form variables in the PayPal driver, WebGUI
+      in-shop credit was not being recieved by PayPal.  This means that Shop users
+      were charged the full amount of the cart instead of the discounted amount.
+
 7.10.15
 --------------------------------------------------------------------
     * WebGUI now depends on Geo::Coder::Googlev3 for it's Map asset

lib/WebGUI/Shop/PayDriver/PayPal/PayPalStd.pm

@@ -265,7 +265,7 @@ sub paymentVariables {
 
         handling_cart        => $cart->calculateShipping,  ##According to https://www.x.com/message/180018#180018
         tax_cart             => $cart->calculateTaxes,
-        discount_amount_cart => -($cart->calculateShopCreditDeduction),
+        discount_amount_cart => abs($cart->calculateShopCreditDeduction),
 
         # When we verify that we have a valid transaction ID later on in
         # processPayment, we'll make sure it's the cart we think it is.