mostly they ask RPRF fee with medical request, but i paid them at the time when i submit my application fee, but i dnt think so you need to worry about that as every is fine at your side. So relax
to avoid delay, you can pay and send it together with your passport..anyway, they will ask you to pay it sooner or later, might as well pay it sooner... although sending passport without RPRF is just fine too... but again, since no one is exempted to pay, they will still ask you to pay for RPRF later which may cause a bit of delay..hope this helps