The $90 fee is for the Corporate card to participate in Membership Rewards, not for the card itself. Some employers block participation in MR altogether. Once upon a time the Corporate Membership Rewards fee was waived if you held a personal Platinum card (rather than Green or Gold), but I dimly recall this changed. I hope someone else who has a Corporate card will be able to explain how it works currently.
Have you been earning rewards, and were you previously charged the $90 fee on your Corporate card account?
Yes, I have been earning points on my corporate card.
Yes, I was previously charged the $90 fee on my corporate card account (immediately after notifying them over the phone that I wished to participate in the program).