Calculated max value by using group by for multiple columns

Anonymous ,

If I understand this correctly, you are creating a new table. I used SUMMARIZE and LOOKUPVALUE

new = SUMMARIZE('Table','Table'[ID Offer],'Table'[ID Client],"AMT",max('Table'[Amount])),
==
Lookup = LOOKUPVALUE('Table'[Rev],'Table'[Amount],new[AMT],'Table'[ID Offer],new[ID Offer],'Table'[ID Client],new[ID Client])

Let me know if you have any questions.

If this solves your issues, please mark it as the solution, so that others can find it easily. Kudos are nice too.
Nathaniel

 Will post pbix shortly.