As far as I can see from the logs of incoming requests to create an order for 07.03 there was such a request with such a ttn number
[ordercode] => 78477
[source] => platformaNT
[sum] => 159
[deliveryid] => 1
[customorder_deliveryNote] => 20450356211447
the value with customorder_deliveryNote will be written in an additional field with the key deliveryNote, but you want to write the invoice number in the standard field, for this the value must be passed with the key deliverynote
request fragment will look like this
http://boxurl/api/orders/add/?deliveryid=1&source=platformaNT&ordercode=...You can always see an example of a request and variables that can be used in the API on the page
https://crm-onebox.com/en/api/