Gateway MQTT payload not valid

[UiGuy]

Hi,

I am getting this error message on gateway event up.

*** PAYLOAD IS NOT VALID JSON DATA *** 

Illegal character ((CTRL-CHAR, code 23)): only regular white space (\r, \n, \t) is allowed between tokens
 at [Source: java.io.StringReader@345fdb0d; line: 2, column: 2]

the topic for this is eu868/gateway/REDACTED/event/up

The gateway itself is a Laird Sentrius (outdoor) connected over port 1700 (Semtech packet forwarder)

The device event is however showing the correct JSON
(application/REDACTED/device/REDACTED/event/up)

My chirpstack-gateway-bridge.toml looks like this:

# See https://www.chirpstack.io/gateway-bridge/install/config/ for a full
# configuration example and documentation.

[integration.mqtt.auth.generic]
servers=["tcp://mosquitto:1883"]
username=""
password=""

[integration.mqtt]
event_topic_template="eu868/gateway/{{ .GatewayID }}/event/{{ .EventType }}"
state_topic_template="eu868/gateway/{{ .GatewayID }}/state/{{ .StateType }}"
command_topic_template="eu868/gateway/{{ .GatewayID }}/command/#"

[integration]
# Payload marshaler.
#
# This defines how the MQTT payloads are encoded. Valid options are:
# * protobuf:  Protobuf encoding
# * json:      JSON encoding (easier for debugging, but less compact than 'protobuf')
marshaler="protobuf"

Any help appreciated.

[Orne Brocaar]

at [Source: java.io.StringReader@345fdb0d; line: 2, column: 2]

This is not an error coming from ChirpStack, it comes from a Java application.