Difference on Monthly precipitation of SEAS 5 data when computed on CDS and directly on ECMWF portal.

Dear forum,

we extracted monthly accumulated rainfall from SEAS5 provided by CDS by using:

'seasonal-monthly-single-levels',
    {
        'originating_centre': 'ecmwf',
        'system': '5',
        'variable': 'total_precipitation',
        'product_type': 'monthly_mean',
        'year': '2016',
        'month': '10',
        'leadtime_month': [
            '1',

        ],
        'area': [
            45, -180, -45,
            180,
        ],
        'format': 'netcdf',
    },
    'download.netcdf')

And we compared to the monthly rainfall extracted directly from the ECMWF portal by using this api:

server = ECMWFService("mars")

def retrieve_s5():
    year = 2016
    month = 10
    day = 1
   startDate = '%04d%02d%02d' % (year, month, day)
   target = "ecmwf/s5_forecast_%04d%02d.nc" % (year, month)
            requestSteps = '745'
            print("Run for " + startDate)
            s5_request(startDate, requestSteps, target)

def s5_request(startDate, requestSteps, target):

    server.execute({

       "class": "od",

       "date": startDate,

       "expver": "1",

       "levtype": "sfc",

       "method": "1",

       "number": "00/to/24",

       "origin": "ecmf",

       "param": "228.128",

       "step": requestSteps,

       "stream": "mmsf",

       "system": "5",

       "time": "00:00:00",

       "type": "fc",

       "grid": "1.0/1.0",

       "format": "netcdf",

       },target)

We then compare the two netcdf generated and we got differences ? Any explanations ?

Thank you very much