HI All,
I'm also in same boat, this is my experience.
US resident, T-mobile customer.
Recently got Venture-X, trying to explore options in the app.
Came across the convert rewards in CapitalOne Travel. Faced same issue as others.
Tried calling customer care more than 10 times in last 4-5 days. Every time fed up explaining the same to Air travel agent and their only response is, "I can help you, with booking a flight".
Today Agent told, its a issue with app update, please try after 1-2 days.

I was like, WHattttt.