Why does this script fail? x is a list with 200 RICs and attributes contains 22 fields. It even fails with chunksize=1.

chunksize = 5
i=0
w,err=ek.get_data(x[i:i+chunksize], attributes, { 'SDate': 0, 'EDate': -5, 'FRQ': 'FY', 'Curn': 'EUR'})    
with open('SAMPLE.csv', 'a') as f:
        w.to_csv(f, sep=';',decimal=',')
for i in range (chunksize, len(x), chunksize):
    print(i)
    w,err=ek.get_data(x[i:i+chunksize], attributes, { 'SDate': 0, 'EDate': -5, 'FRQ': 'FY', 'Curn': 'EUR'})
    with open('SAMPLE.csv', 'a') as f:
        w.to_csv(f,  sep=';',decimal=',',header=False)

returns

5
10
15
20
Backend error. 400 Bad Request

Looking forward to your comments.