Error when attempting to port Google Voice number

Firstly,  I'm a happy Xfinity Mobile customer.   Currently have 4 lines,  and couldn't be happier with the service and pricing.   Here's my issue:

I'd like to take advantage of a current promotion (Free iPhone SE with new line activation and number port from another service provider) I have 2 Google Voice numbers that I'm attempting to use in order to qualify for the deal.   When going through the ordering process online,  I'm asked to supply the phone number and carrier of the number to be ported.  Oddly enough,  1 of the Google Voice numbers is eligible but the other Google voice number is not.  I receive the following error during ordering:

"This number is ineligible for transfer. Try a different number or select new number."

Both Google Voice numbers have been "unlocked" which was completed with a small fee I paid to Google to do this.   One more data point is the GV number that works, is an older GV number,  while the one that fails,  is a new GV number.  Not sure if that matters or not, but worth a mention.

Has anyone received that error above while attempting to go through the ordering process online?  If so,  what was the fix?