combine 2 worksheets together with Pivot

Hi, I tried to combine 2 worksheets together.
made them 2 tables and i can find them in pivot table. however, when i clicked "relationship" in the ribbon of the excel and tried to connect 2 together by setting "contract No"as the column to connect them, it always says "both selected columns container duplicate values. At least one of the columns selected must contain only unique values to create a relationship between the tables".

What I am trying to do is, one sheet is for incoming inventory with one contract number. the other sheet is for outgoing orders. several orders can be under one contract. it means, we import a bigger tonnage and divide them into deliveries with smaller quantities, and I also would like to know the remaining quantity for each contract after several deliveries.

i don't know what i have done wrong but I couldn't connect them.
Could someone tell me what I should do please?
Thank you!

Hi danielpak,
Convert each dataset to a table (Ctrl + T). In the attached they are now Table1 & Table 2.
Create a Pivot table from one of the tables and click "Add this data to the Data Module" (bottom of dialog box).
On the Pivot Field Selector, on the top right under the heading "PivotTable Fields" you will see; Active All
Click Edit Relationship. Link the tables (see screenshot).
In the Field Selector you now can see the Table1 and Table2. Expand to select fields you need.
Trust this helps.

Using Power Query (Available on the Data Tab), I brought each table into PQ. Removed columns not required (kept Contract Nr. and Bags.) Joined the two tables with a Left Inner Join. Netted In and Out. See the attached file.Review PQ

In the attached file
Click on any cell in the new table
On the Data Tab, click on Queries & Connections
In the right window, double click to open Query
Review PQ steps