SignFast is built and maintained by one person. Real human replies, usually within 24 hours.
My signature won't save. Make sure you have at least a few MB of free space on your device. Signature data is tiny, but the app writes a backup of your key on first launch.
I bought Pro on my old phone — how do I restore it? Open Settings → Restore Purchases. SignFast asks Apple for your purchase history and unlocks Pro for free on any device signed into the same Apple ID.
Does SignFast work in airplane mode? Yes. The app is designed to work without any network. The only time it talks to the internet is during an in-app purchase, which uses Apple's StoreKit.
Is the signature legally binding? SignFast applies a cryptographic signature you can verify yourself. Whether it counts as a "qualified electronic signature" in your jurisdiction depends on local law. For high-stakes legal documents, consult a notary or a qualified e-signature service.