Add fields to header of RDLC Sales Invoice Report Layout 206

Good day.

I am new to the forum, so please bare with me.  I will try explain my issue.

I am customizing a Sales Invoice RDLC 206 layout and I am trying to add the following 2 fields to the header: (BilltoCustNo_SalesInvHdr & ShipToAddr1)

This is what I have tried to do:

BilltoCustNo_SalesInvHdr (which is expression value =Code.GetData(9,1)) to SelltoCustNo_SalesInvHdr (which is not part of the code on the hidden expression in the table in the body of the mail).  I have tried to add the SelltoCustNo_SalesInvHdr to this record and see if it works but it doesn't seem to find it, when you run the preview or the invoice. 

What am I doing wrong that the field cannot be added to the hidden table in the body to appear? If I delete all the fields in the hidden body they all disappear from the header - so the code is updating. I add just the SelltoCustNo_SalesInvHdr back and I get no error it just runs but that field is blank? I have tried replacing line 9 with the Sellto field but it then makes the preview blank.

The code I am talking about can be found in the table properties under visibility, show or hide based on expression in the hidden table top left of the body of the invoice report layout. 

Any assistance in getting the fields into the header of the Invoice report layout would be awesome! Steps would also be great.

Thanking you in advance for a solution.

Kind Regards