Trouble with LookUp in merging 2 dataset

Dear all

I have the following Expression in a Tablix called CustomerInfo

=Lookup(Fields!ab_primarycontactid.Value,Fields!contactid.Value, Fields!fullname.Value, "Contact")

The CustomerInfo Table as a its source pointing to a QuoteDataset which contains ab_primarycontactid field

I try to retrieve the primary contact information located in a Dataset "Contact" but the lookup field return empty.

Each dataset is corresponding to 2 different FetchXML content

Any idea why I cannot retrieve the fullname ofmy primary contact ?

thanks ofr your help

regards

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