Most transfer fees are paid in instalments over several years rather than in one payment, with the schedule written into the deal. The headline figure is the total, so two clubs quoting the same fee can be paying very different amounts in the first year.
The structure is often the real negotiation. A selling club that needs cash now will accept a lower total in exchange for more of it up front, and a buying club short of immediate room will pay a higher total for the right to spread it. Both sides can then announce a number that suits them.
This is separate from amortisation, and the two are easy to confuse. Instalments are when the money actually leaves the bank; amortisation is how the cost is recorded in the accounts each year. A fee can be paid over two years and accounted for over five.
Selling clubs sometimes take payment risk into account as well, because instalments due over several years depend on the buying club still being able to pay them. Deals occasionally include guarantees or a discount for early settlement for exactly that reason.