The speed doesn't show
Allow location for Speedometer Widget in Settings › Privacy & Security › Location Services. If Location Services is off for the whole iPhone, turn it on there first. GPS needs a clear view of the sky, so the speed can take a moment to appear and can drop out in tunnels.
The Live Activity doesn't appear
The Live Activity is part of Pro and starts with a trip. Check that Live Activities are on in Settings › Speedometer Widget. On CarPlay it appears on the Dashboard with iOS 26 or later, and on Apple Watch it appears in the Smart Stack.
Cancel or manage your subscription
Open iPhone Settings, tap your name, then Subscriptions. Cancel at least 24 hours before the renewal date to stop the next charge. Deleting the app does not cancel it. For a refund, use reportaproblem.apple.com.
Restore Pro on a new phone
Tap Restore on the subscription screen while signed in to the same Apple Account. It never charges you.