The same rpc invocation via restconf using xml works. Nothing appeared in karaf.log (root set to INFO).

This is working xml input:
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<input xmlns="urn:opendaylight:bulk-flow:service">

<bulk-flow-item>

<node xmlns:inv="urn:opendaylight:inventory">/inv:nodes/inv:node[inv:id="openflow:1"]</node>
<table_id>0</table_id>

<cookie>142</cookie>
<priority>0</priority>
<strict>false</strict>
<flags>SEND_FLOW_REM</flags>
<hard-timeout>0</hard-timeout>
<idle-timeout>0</idle-timeout>
<instructions>
<instruction>
<apply-actions>
<action>
<dec-nw-ttl/>
<order>0</order>
</action>
</apply-actions>
<order>0</order>
</instruction>
</instructions>
<match>
<ethernet-match>
<ethernet-type>
<type>2048</type>
</ethernet-type>
</ethernet-match>
<ipv4-destination>10.0.1.0/24</ipv4-destination>
</match>
</bulk-flow-item>
</input>

This is corresponding json (not working):
{"input": [
{"bulk-flow-item": {
"node": "/opendaylight-inventory:nodes/node[opendaylight-inventory:id=\"openflow:1\"]",
"cookie": 142,
"flags": "SEND_FLOW_REM",
"hard-timeout": 0,
"idle-timeout": 0,
"instructions": {
"instruction": [{
"apply-actions": {
"action": [
{
"dec-nw-ttl": {},
"order": 0
}
]
},
"order": 0
}]
},
"match": {
"ethernet-match": {
"ethernet-type":

},
"ipv4-destination": "10.0.4.0/24"
},
"priority": 0,
"table_id": 0
}}
]}