EONIA fixing value is not available since 2020-12-22.
df, err = ek.get_data(['EUROSTR=','EONIA='],['TR.FixingValue','TR.FixingValue.date'], {"Sdate": '2020-12-20',
"Edate": '2020-12-28'})
df
Instrument Fixing Value Date
0 EUROSTR= -0.557 2020-12-21T00:00:00Z
1 EUROSTR= -0.558 2020-12-22T00:00:00Z
2 EUROSTR= -0.559 2020-12-23T00:00:00Z
3 EUROSTR= -0.555 2020-12-24T00:00:00Z
4 EUROSTR= -0.553 2020-12-28T00:00:00Z
5 EONIA= -0.472 2020-12-21T00:00:00Z
6 EONIA= -0.473 2020-12-22T00:00:00Z
7 EONIA= NaN 2020-12-23T00:00:00Z
8 EONIA= NaN 2020-12-24T00:00:00Z
9 EONIA= NaN 2020-12-25T00:00:00Z
10 EONIA= NaN 2020-12-28T00:00:00Z