I'm trying to perform a potentiometric titration to determine the redox potential of a $\ce{Fe^3+|Fe^2+}$ couple. To do this, I am using an $\ce{Ag|AgCl}$ electrode connected to an inert $\ce{Pt}$ electrode, which is submerged in a solution containing $\ce{Fe^3+}$ ions. I then titrate it with $\ce{Co^2+}$, which reduces it to $\ce{Fe^2+}$. The reference and inert electrode are connected with a standard voltmeter.

What I don't understand is **why** the inert electrode measures the redox potential of the $\ce{Fe^3+|Fe^2+}$ couple. As per my understanding, there is an electron flow from the reference electrode into the inert electrode, which would get accepted into the Fe solution, but now, the transfer of electrons is only between the $\ce{Co^2+}$ and $\ce{Fe^3+}$ ions, so what happens to that electron? Can someone explain exactly how the redox potential of the $\ce{Fe^3+|Fe^2+}$ couple gets measured, with reference to electron transfer between the reference and inert electrodes?