OK. I figured it out.

So, AMEX will give you statement credits of up to $120 for Uber One. Got that. Easy.

About 1 month ago, it turns out that I signed up for a free Uber One promo - pitched to me by Uber. I signed up thinking it was basically signing up for the (eventual) Uber One benefit. About 1/2 a week ago,unbeknownst to me, Uber said, OK one month promo over - sign him up for Uber One annual. Charge him for Uber One annual. It turns out that, in my haste to sign up for the free promo, I didn't pay attention to the Uber One membership settings ... Account --->. Uber One ---> Manage Membership ---> Payment Details which had my payment method set to ping/pay using my Uber cash balance.

Within that Payment Details / payment method setting, when I rejoined Uber One (on a monthly basis, $9.99 per month) I had to be sure to check/select my Amex Plat card as my payment method.

Problem solved. As I tell my kids "Pay attention" and most of life's problems will never come your way.