take this from their official docs :
import { useState } from 'react';
import { useOkto } from '@okto_web3/react-sdk';

function EmailAuthentication() {
const oktoClient = useOkto();

const [email, setEmail] = useState('');  
const [otp, setOtp] = useState('');  
const [token, setToken] = useState('');  

async function handleSendOTP() {  
    try {  
        const response = await oktoClient.sendOTP(email, "email");   
        console.log('OTP Sent:', response);  
        setToken(response.token);  
    } catch (error) {  
        console.error('Error sending OTP:', error);  
    }  
}  

async function handleResendOTP() {  
    try {  
        const response = await oktoClient.resendOTP(email, token, "email");   
        console.log('OTP Resent:', response);  
        setToken(response.token);  
    } catch (error) {  
        console.error('Error resending OTP:', error);  
    }  
}  

async function handleVerifyOTP() {  
    try {  
        const session = await oktoClient.loginUsingEmail(email, otp, token, (session: any) => {   
            localStorage.setItem("okto_session", JSON.stringify(session));   
        });   
        console.log('Login Successful:', session);  
    } catch (error) {  
        console.error('Error verifying OTP:', error);  
    }  
}  

return (  
    <div>  
        <input type="email" placeholder="Enter email" value={email} onChange={(e) => setEmail(e.target.value)} />  
        <input type="text" placeholder="Enter OTP" value={otp} onChange={(e) => setOtp(e.target.value)} />  

        <button onClick={handleSendOTP}>Send OTP</button>  
        <button onClick={handleResendOTP}>Resend OTP</button>  
        <button onClick={handleVerifyOTP}>Verify OTP</button>  
    </div>  
);  

}
Success Response
Note

For error handling:

Use the error code to debug issues. Check out the SDK errors and warnings documentation
For help, navigate to the troubleshooting guide to contact support
Method Overview
Method Description
async OktoClient.sendOTP Sends an OTP to the user's email
async OktoClient.resendOTP Resends an OTP using a previously generated token
async OktoClient.loginUsingEmail Verifies the OTP and logs in the user
Send OTP
async OktoClient.sendOTP(contact: string, method: "email") sends the OTP to the specified email address.

Parameters
Parameter Type Description Required
contact string User's email address Yes
method string OTP delivery method (email or whatsapp) Yes
Response
Success Response

Field Name Type Description
result Promise<EmailSendOtpResponse> Resolves with a success response if the OTP is sent successfully
Response Type
Resend OTP
async OktoClient.resendOTP(contact: string, token: string, method: "email") resends the OTP using the previously issued token.

Parameters
Parameter Type Description Required
contact string User's email address Yes
token string The token received from the previous sendOTP request Yes
method "email" OTP delivery method (email or whatsapp) Yes
Response
Success Response

Field Name Type Description
result Promise<EmailResendOtpResponse> Resolves with a success response if the OTP is resent successfully.
Response Type
Login Using Email
async OktoClient.loginUsingEmail(contact: string, otp: string, token: string) verifies the OTP against the provided email and logs in the user. If successful, returns the user’s Smart Wallet Address.

Parameters
Parameter Type Description Required
contact string User's email address Yes
otp string OTP sent to the user email address Yes
token string The token received from the previous sendOTP request Yes
Response
Success Response

Field Name Type Description
result Promise<Address> Returns the user's Smart Wallet Address on successful login

also add a demo mode with sample otp "123456" in case the api call does not work