I can place order via freedom API but I want to edit existing order and place invoice from existing order

What is the schema for updating existing order ?

Endpoint to place invoice from existing order:

 http://127.0.0.1:5000/freedom.core/DATABASENAME/SDK/Rest/SalesOrderExistingProcessInvoice

Endpoint to edit existing order:

 http://127.0.0.1:5000/freedom.core/DATABASENAME/SDK/Rest/SalesOrderExistingPlaceOrder