# Ratepay API Payment-Change Logic

**Manage customer requirements and customer complaints with ease!**

The gateway `<operation>PAYMENT_CHANGE` is used to manage

- shopping cart modifications
- (partial) cancellations
- (partial) returns
- goodwill refunds


Learn how to use the `<operation>` element correctly. On the next pages we are going to modify **one single transaction** multiple times.

## Purchase Order

Every transaction starts with a purchase.


```xml
<operation>PAYMENT_REQUEST</operation>
```

### Assumption

Let's imagine a shopper bought three items. One item has a discount. Then there are some shipping fees and our customer redeemed a voucher. The shopping basket amount is 305 Euros in total.

Try to reconstruct the total basket value.

**XML request**


```xml
PAYMENT_REQUEST.xml

<shopping-basket amount="305" currency="EUR">
	<items>  
		<item article-number="A" quantity="2" tax-rate="19.00" unit-price-gross="100" discount="-10" description-addition="Rot">Bed Linen</item>
		<item article-number="B" quantity="2" tax-rate="19.00" unit-price-gross="40" description-addition="100x200">Towel</item>
		<item article-number="D" quantity="2" tax-rate="19.00" unit-price-gross="25">Scarf</item>
	</items>
	<discount unit-price-gross="-10" tax-rate="19.00">Voucher</discount>
	<shipping unit-price-gross="5" tax-rate="19.00">UPS Standard</shipping>
</shopping-basket>
```

**Result**

|  | # | Price | Cart |
|  --- | --- | --- | --- |
| `<item>` | A | 90 € | 2 |
| `<item>` | B | 40 € | 2 |
| `<item>` | D | 25 € | 2 |
| `<discount>` |  | -10 € | -10 € |
| `<shipping>` |  | 5 € | 5 € |