INVALID SERVICE-TYPE KANNEL

Hello,
I have an issue I have configured kannel and am able to bind to SMSC
provider. Not when I send message to SMSc Provider am getting an
error message in log as below
2018-11-09 14:00:20 Receive DLR [SMSC:airtel] [SVC:] [ACT:] [BINF:] [FID:]
[META:?smpp_resp?] [from:zzzz] [to:260976298808] [flags:-1:-1:-1:-1:16]
[msg:36:NACK/0x00000015/Invalid Service Type] [udh:0:]


My question where is that put?

I have asked SMSC provider and the have told me service-type=smpp

I added to config file but still get same error

TCPDUMP from smsc provider show they are receiving NOBAL as service type
from our end.
please help below is config

group = smsc
smsc = smpp
smsc-id = zoned
host = 172.xx.xx.xx
port = 5xx
interface-version = 34
smsc-username = xxxxxx
smsc-password = xxxxxx
system-type = smpp
service-type = smpp
source-addr-ton = 5
source-addr-npi = 0
dest-addr-ton = 1
dest-addr-npi = 1
transceiver-mode = true
throughput = 40


Thanks

Chris Kamutumwa