SQL can do it simply:
proc sql;
create table want as
select
Product,UWYear,AccidentYearMonth,MasterPolicy,
PolicyHolder,ProducerName,ClaimNo,Coverage,
sum(lossincurred) as lossincurred
from have
group by
Product,UWYear,AccidentYearMonth,MasterPolicy,
PolicyHolder,ProducerName,ClaimNo,Coverage
;
quit;
Note that -2,547,181 is already a valid numeric value, if the column type is numeric. Otherwise, convert by using the comma. informat:
data test;
charvar = "-2,547,181";
numvar = input(charvar,comma12.);
run;