JSON Composition for sending inbound invoice:

{
	*"auth" : key obtained in get/auth method
	*,"invoice" :
		{
			"key" : invoice key
			,"number" : invoice number
			,"serial" : invoice serial number
			,"purpose" : 1/normal entry, 2/return (default 1)
			,"note" : reason for return
			,"data" : base 64 of the purchase Nfe XML
		}
		,"products":
		[
			{
				"code_invoice": client/supplier SKU code
				,"code_to": product code registered in FMS
			}
		]
}

Returns with:
{
	"code" : integer – system execution code
	,"message" : text – "OK" or detailed error message
	,"id": integer – internal invoice number
}

Code:
200: purchase invoice processing (stock may take up to 1h to reflect)
400: fiscal invoice contained errors, check "message" tag
401: invoice already inserted
402: SKU missing mandatory mapping
500: invalid auth
501: user without authorization to insert purchase invoice