LTE modem - No IP address

Hi,    I have managed to configure a Huawei E3372 LTE modem on our Fortigate 60E (v6.0) and all the test applications seems OK - but my network interface does not obtain an IP address.  Even though it have taken all day to read the documentation and to figure out how to configure the device - the configuration itself is rather simple. 

config system lte-modem
 set status enable
 set apn "internet"
 set modem-port 0
end

I had to set the modem port to make this test return an IP address from the ISP. And now the test works as it should and returns an valid IP from the ISP (the IP below is scrambled for privacy) 

diagnose test application lte 6

+CGPADDR: 1,"99.23.81.62"

OK

So everything seems to be working just fine - but when i check my WWAN interface - it does not have an IP address. Shouldn't it just have the same IP that i get when running the test against the LTE Modem?

fnsysctl ifconfig wwan
wwan Link encap:Ethernet HWaddr 00:1E:10:1F:00:00
 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
 RX packets:0 errors:540 dropped:0 overruns:0 frame:0
 TX packets:193 errors:0 dropped:0 overruns:0 carrier:0
 collisions:0 txqueuelen:1000
 RX bytes:0 (0 Bytes) TX bytes:112870 (110.2 KB)

I notice an error-counter climbing on RX in ifconfig. But i don't know what to do about it. If i run debug, the DHCP client just returns with "failed" when requesting an IP address. Do you have any ideas on what i should look for?