SUMIFS with Text and Date criteria

Try

=SUMIFS(B:B,C:C,"simon",A:A,">="&DATE(2018,5,1),A:A,"<="&EOMONTH(DATE(2018,5,1),0))

Or

in E1

=SUMIFS(B:B,C:C,"simon",A:A,">="&D1,A:A,"<="&EOMONTH(D1,0))

where D1=01/05/2018