An invoice can contain some credits (sometimes referred to as ```cba``` for credit balance adjustment). These are represented in various ways, depending on the object:

* For ```InvoiceJsonSimple``` (https://github.com/killbill/killbill/blob/master/jaxrs/src/main/java/com/ning/billing/jaxrs/json/InvoiceJsonSimple.java), which doesn't contain invoice items, ```creditAdj``` represents the sum of all credits on that invoice.
* For ```InvoiceJsonWithItems``` (https://github.com/killbill/killbill/blob/master/jaxrs/src/main/java/com/ning/billing/jaxrs/json/InvoiceJsonWithItems.java), besides the ```creditAdj``` field, there is also a collection of ```items```. Some of the items can represent credits.
* For ```InvoiceJsonWithBundleKeys``` (https://github.com/killbill/killbill/blob/master/jaxrs/src/main/java/com/ning/billing/jaxrs/json/InvoiceJsonWithBundleKeys.java), besides the ```creditAdj``` field, there is also a collection of ```credits``` (https://github.com/killbill/killbill/blob/master/jaxrs/src/main/java/com/ning/billing/jaxrs/json/CreditJson.java), with a ```creditAmount```.