Support
Nightfan has no account and no sign-in, so there is nothing to reset and nothing to recover. Most questions are answered here.
Restoring a purchase
Open Nightfan, go to Settings, and tap Restore purchases. On a new phone, sign in with the same Apple ID or Google account you bought with first.
Cancelling a subscription
Subscriptions are managed by the store, not by the app. On iPhone: Settings, your name, Subscriptions. On Android: Google Play, Payments & subscriptions. Cancel at least 24 hours before the renewal date to avoid being charged.
The sound stops when the screen locks
Check that Low Power Mode is off, and that Nightfan is allowed to run in the background. Sound keeps playing through a phone call and resumes afterwards.
Safe volume for a baby
Keep the phone at least two metres from the cot and the volume at or below 50 decibels, about a quiet conversation. The volume limiter in Settings caps it for you, and it is on by default.
Still stuck
Write to hbh@tekbh.com and a person will answer.