Hi David - the minimum for a token transfer is indeed 0.21 VTHO, so it should send providing you leave that amount for gas fees.

Is your wallet updated to the latest version? Please try and update if not. If the issue persists, you can submit a ticket directly to the team by going to 'settings', then 'about' on the VeWorld mobile wallet.

Alternately, there is a channel on Discord where you ca ask developers directly: discord.gg/vechain