Answer
Web offers the subscription flow. Native iOS and Android show AI Usage Limit Reached and direct you to manage usage in a browser. You can explicitly turn @ai off to send an ordinary People message.
Free trial requests need at least $0.05 for Text, $0.15 for Image, $0.25 for a song, $1.00 for five seconds of Video or $2.00 for ten seconds. Meeting a starting balance does not fix the final Text cost, which depends on actual usage.