Order form split testing is done from the Content Menu Option > Order Forms Submenu Option
In the top right corner hit the + Icon to create a new Order Form Split test.
Name the Order Form Split test and you will get to the configuration screen.
Here you are provided a short code ( which can contain parameters to pass to the split tested paylink )
EG: $paylink form=2
Then you will be asked to provide the payment links that will be split tested.
Versions ( add at least one version to activate the form )
Note: It is possible to pass parameters to the short code that will get appended to the paylink, like cbitem=xcxx or vtid=somevtid EG: $paylink form=2 cbitem=xcxx vtid=somevtid