Merge 3 Data source-2 unrelated

I have 3 data source

GL Table: - Serial #; Date; Trans Amt (3 fields)
Serial Nbr Table: Serial #;Item Nbr (2 Fields)
Item Info Table: Item Nbr; Item Model (2 fields)

Merge on GL and Serial Nbr tables-Serial#
Merge on Serial Nbr and Item Info-Item #

I’d like all fields in GL report plus Item Model or $ by model however I get a DATASYNC error. I’ve tried making detail variables but still error as soon as I bring in a field not in the “merge” like date. I’ve had this struggle for years now but think there must be something I’m missing.

what did you select as associated-dimension in the “Date”-detail-variable ?

Sorry-I did not describe correctly. I did not do a detail variable for the date field as it would be a multivalue with multiple dates. I’d like the GL table to be all rows and the 2 other reports supporting details.