Where did you enter your requisition - in Purchasing or iProcurement module? And did you pull the Contract Number from a LOV or simply entered it as like a free-text?
I will endeavour to answer it based on your comments received.
Dont check the contract column on the Requisition line summary, instead verify the column source document & source document number. Normally these column is hidden and you can view by folder--> show field. The contract number on the requisition summary for oracle contracts. Dont get confuse with iProcurement column name and base requisition form.
I am assuming you entered Contract Number in Requisition Screen > Source Details > Contract Num field
Once you are in Requisition Lines Summary , Go to Folder > Show Field > Select Contract Num field to see the Contract number you selected.
Contract Num field is generally hidden in Requisition lines Summary, hence you need to use Folder Tools to make it visible.