Splunkforwarder HEC input/output to another splunkforwarder

[fsource]

Hello,

i'm triing to use an UF to forward HEC from internet data to another UF in our DMZ

look like :

httplistner input (UF1) httpout output  --> httplistner input (UF2 in DMZ) S2S output --> Splunk enterprise in lan

if i curl both of http listener i got success, 

curl -k -u "x:TOKEN" "https://UF1:8088/services/collector/event" -d '{"event": "Hello, world!"}'
{"text":"Success","code":0}

curl -k -u "x:TOKEN" "https://UF2:8088/services/collector/event" -d '{"event": "Hello, world!"}'
{"text":"Success","code":0}

But i got events in my splunk indexeur only on the second curl, the first one look like the output never forward to the UF2... 

Nothing in both uf1-2 logs about errors. 

My /opt/splunkforwarder/etc/system/local/outputs.conf on UF1 look like:

[tcpout]
defaultGroup = default-autolb-group
disabled = 1

[httpout]
disabled = 0
httpEventCollectorToken = MYTOKEN
uri = https://UF2-IP:8088
batchSize = 65536
batchTimeout = 5

Thks for help !!

Flo V.