Concatenating result from multiple rows from a lookup table

[arikofather]

I have these two tables:

I want to create a new column called Members in OPP table to concatenate all occurences of Initials in DM.

Result to look like this:

Glad to get the Dax 

[DataInsights · Accepted solution]

@arikofather,

Try this calculated column in OPP table:

Members = 
CONCATENATEX ( RELATEDTABLE ( DM ), DM[Initials], ", " )