Datasource Load

I have successfully tested datasource load using a grid and  excel source. My problem is; there is a parent and child relationship to the data I want to submit i.e.

Login credentials

Invoice Header

Matching orders

I am trying to loop to populate the order numbers

The xml file is attached:

The API expects the total order value to equal the invoice value, but doea not wait until all the data is sent when using the load function.

I do not want to submit one invoice per works order the volume of invoices would be unacceptable.

I am a novice and would prefer not to trawl through all the help documents/videos. If someone would be kind enough to point me in the right direction and hopefully I can work something out.

Thanks in anticipation