The full adjudication can be found here:
Basically, all properties to rent need to show the cost of how much it will be to rent the property in addition to the rent i.e any administration charges and this is also to be shown on Rightmove. Realistically this will mean on all property portals.
We would advise to list any admin fees in a bullet point, that way it is clear and will be passed to all portals, your own website and also shown on any window cards (thus covering all bases).
Do remember that all advertisements of sales and lettings and your own services are governed by the ASA.