Send subform data with posturl

Send subform data with posturl

Hi,

Does anyone know how (or even if it's possible) to send data from a record that includes the related subform data to an external api using posturl or similar method?  I need to populate my external accounting application with invoices and their related line items from my Creator app.  I'm able to populate the invoice data correctly but I'm not sure how to get the related subform data (line items) over as well and can't seem to locate anything specific in the forum or help guides that demonstrates it.

Rob