Thank you so much for all replies.
How about the transaction fee? Any wallet with the zero transaction fee?
Note: Wallet (non-custodial) doesn't charge the transaction fee, you are paying the network fee.
There are plenty of wallets which will let you sign and broadcast transactions with zero transaction fee, with or without below relay fee! error. @PowerGlove has beautifully explained above what relay fee means. But when you are making wallet, the main stress should be on usability. A good fee suggestion algorithm and low/high fee warnings according to it are the desirable features from the wallet. If that system is in place then the wallet can let the users select any fee (even zero if they want).