Group By function in Oracle

Hi Team,
I am trying to use a simple Group by code as shown, ...But don't need to do a Group BY on ISIN..(Varchar)...But when I remove that...I get error saying not a Groupby function...Can I just do a group by based on first two columns. ?

select distinct G.CLIENT_ID,G.YEARMONTH, D.ISIN,SUM(G.ACCOUNT_CBV) as ACCOUNT_CBV, SUM(G.TOTAL_REVENUES) as TOTAL_REVENUES from GMIS G, DEPOT D 
where G.CLIENT_ID = D.CLIENT_ID 
GROUP BY G.CLIENT_ID,G.YEARMONTH,D.ISIN order by Client_ID;

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