I tried to create invoice with api.
I send the creating xml code and get the result xml from FB. But I always get the wrong invoice id which is different from the real one in my FB.

IE: An invoice id 00000072 was created in my FB. but the result xml is 00000060, which is 12 less than the real one.
Below is the difference between 2 ids.
The real one in FB, the result xml
00000072,    00000060
00000073,    00000061
00000074,    00000062
00000075,    00000063
00000076,    00000064
00000077,    00000065

My code is as below:
<request method="invoice.create">
<invoice>
<client_id>1618</client_id>
<po_number>Test9081201</po_number>
<notes>Test1 line1</notes>
<discount></discount>
<lines>
<line>
<name>40010-ChEx WB</name>
<description>Test90812011 Lb shipment to China via Chex</description> <unit_cost>12.58</unit_cost>
<quantity>1</quantity>
<tax1_percent></tax1_percent>
<tax2_percent></tax2_percent>
</line>
<line>
<name>40035-ChExFS</name>
<description>ChEx Express Fuel Surcharge, 4.98%</description> <unit_cost>12.58</unit_cost>
<quantity>0.0498</quantity>
<tax1_percent></tax1_percent>
<tax2_percent></tax2_percent>
</line>
</lines>
</invoice>
</request>

Who can help me?