httperf: did not recognize arg #49

httperf --server=localhost --port=9081 --method=POST --uri=/bid/123 --add-header="Content-Type: application/json\n" --wsesslog=1000,100,http_perf.txt

httperf --client=0/1 --server=localhost --port=9081 --uri=/bid/123 --send-buffer=4096 --recv-buffer=16384 --add-header='Content-Type: application/json\n' --method=POST --wsesslog=1000,100.000,http_perf.txt
httperf: warning: open file limit > FD_SETSIZE; limiting max. # of open files to FD_SETSIZE
httperf: did not recognize arg '"ssp1-27009141-1485848975137","at":' in http_perf.txt

Contents of file http_perf.txt
contents={"id": "ssp1-27009141-1485848975137","at": 2,"imp": [{"id": "1","bidfloor": 13.521766169371157,"bidfloorcur": "RUB","banner": {"pos": 0,"h": 100,"w": 300},"secure": 0}],"site": {"id": "10930","domain": "warfiles.ru","ref": "http://warfiles.ru/show-142725-rossiya-vpervye-ispytala-noveyshuyu-aviabombu-drel-v-sirii.html","publisher": {"id": "9886"},"ext": {"place_id": 79170},"cat": ["IAB12"]},"device": {"ua": "Mozilla/5.0 (iPad; CPU OS 9_3_5 like Mac OS X) AppleWebKit/601.1.46 (KHTML, like Gecko) YaBrowser/16.11.0.2708.11 Mobile/13G36 Safari/601.1","ip": "84.234.53.206","make": "Apple","model": "iPad","os": "iOS","osv": "9.0","devicetype": 5},"user": {"id": "35e4f8a5-e897-4589-a075-bc2c8acd7e1e","buyeruid": "6331632281203562848","geo": {"type": 2,"city": "Moscow","region": "MD-BD","country": "Russia"}}}

I have tried escaping " with \  , but it did not help either .
Please advise .