When summoning a mount, any mount, the action you are using as shown on the party list is "Chocobo Whistle".

That works for a chocobo, but not for a Coeurl or a suit of Magitek Armour.

It would be best to change the action name to that for the applicable mount, such as "Coeurl Bell", or simply "summon mount" if a common action is mandated by the system.