The error occurs because the 'redirect_url' key is placed inside the 'template_details', which is incorrect. To resolve this, kindly move 'redirect_url' outside of 'template_details', as shown in the updated code snippet below:

const signupConfig = {
    platform_type: 'web',
    redirect_url: '{Redirect_URL}',
    template_details: {
        senders_mail: '[email protected]',
        subject: 'Welcome to %APP_NAME%',
        message: `
            <p>Hello,</p> 
            <p>Click the link below to join %APP_NAME%:</p> 
            <p><a href='%LINK%'>%LINK%</a></p> 
            <p>If you did not request this, please ignore this email.</p> 
            <p>Best regards,</p> 
            <p>The %APP_NAME% Team</p>
        `,
    }
};