Using CRM Java API SDK to insert record into Multi-Select Lookup

I am able to insert records using the Java API SDK except Multi-select Lookup. I know that there is a hidden module associated with the Multi-Select Lookup, in this case "Shopping_X_Members". I am using this code:

ZCRMRecord newMember = new ZCRMRecord("Shopping_X_Members");

newMember.setFieldValue("Members_at_Shopping_Participants", participant);

newMember.setFieldValue("Members", member);

APIResponse zohoNewMember = newMember.create();

where participant or member are either ZCRMRecord or ZCRMEntity

And after the newMember.create() runs, I get an "INTERNAL SERVER ERROR". I'vealso tried

ZCRMRecord newMember = new ZCRMRecord("Shopping_X_Members");

APIResponse zohoNewMember = newMember.create();

Just to see if anything will be created, but no luck, same error "INTERNAL SERVER ERROR".

Is there a special way to create a new record for a multi-record lookup hidden module?