Thanks for the screenshot.
I think this explains what is happening. The Billing page shows that your monthly credits are $0.00 / $5.00, and the remaining $9.94 is under Purchased Credits.
I found a related Vercel Community answer saying that purchased v0 credits require an active paid v0 plan, such as Premium, Team, or Enterprise, to be used. So if your account is currently on the Free Plan, v0 may not let you spend those purchased credits even though they still appear as available and unexpired.
That would explain why v0 says you are out of credits after the monthly credits are used up.
If you do not want to upgrade just to use the purchased credits, I would contact Vercel Help/Billing Support and ask whether they can refund the unused purchased credits or confirm the exact policy for Free accounts.