I've been a happy Ting customer since 2014. Recently I swapped to a Moto G5S Plus on CDMA which I had ordered in the Ting store. When I entered the sim card and IMEI in the Ting desktop dashboard, it gave me that error. I know that a UICC is the ICCID sim card number. I called Ting and spoke with Carlos. He told me that error was because it was not the CDMA sim card which came with the phone. I had received a CDMA and GSM sim card for Ting in the phone box. But I had also ordered another CDMA sim card just to have in my stash. That separate one was the one I was trying to use. So on Carlos' advice, I tried the CDMA sim card which shipped with the phone and it worked.
It would be nice if the Ting dashboard provided this as a likely explanation beyond just:
Equipment does not support UICC but UICC exists
That said, I am very happy with Ting!