How To do data validation for matching entries between 2 cells based on input in 3rd cell

[diddy47]

I would like to apply data validation to cell K3 based on A3

The value of K3 only comes up after a correct numerical code is entered in K4 (based on the formula in K3 referencing Source! )

basically I want the file to reject the entry in K4 if the resulting value on K3 does not match A3

so as to prevent a different user signing off on a time log that is not tied to their ID

as it currently set up any one can sign off any time log entry... (resulting in the signee being different from A3) the goal is so that only the person selected in A3 can successfully enter a code in K4 so that the K3=A3