First, the expression pedal’s 1/4” connector must be a 3-conductor TRS (tip-ring-sleeve) type. Pedals with a 2-conductor TS (tip-sleeve) are usually meant for analog volume control, and won’t work properly.
Even amongst 3-conductor expression pedals, there are two commonly used connection standards. Through the utility app GiOConfig, GiO supports both standards. Please see page 21 of the GiO User's Guide for details.
Apogee has tested the Yamaha FC-7 and the Roland EV-5.