jwt token is giving correct response even I modified JWT

Question

I have implemented the JWT in my spring boot application with the help of This Artical

Here my issue is when I am testing with postman, I need to give the JWT token in headers, I have passed the same to my get method, I am getting the response, When I try to change the last letter of JWT token, then also I am getting the response 200 and getting the data. It means somewhere the JWT implementation getting wrong.

Token is something like below eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiYWRtaW4iOnRydWUsImp0aSI6ImU3MjcyNzY4LTNiYWYtNGNlMi1iYWI4LWMzMmRmM2M0OTEwNiIsImlhdCI6MTYwMDc4NDgyOCwiZXhwIjoxNjAwNzg4NDI4fQ.FVQDZW9chTpmBQhGKBhMlUYz9qTUdh7IRZnVmP7aSn

If I change more than one character at the last of JWT token, then it is giving 401 Unauthorized. If I give only w word at the last of JWT token, then also I am getting 401, When I give other than w then I am getting 200

How can I resolve the same. When I chang any one character then it should identify the change it should give 401

import java.io.Serializable;
import java.util.Base64;
import java.util.Date;
import java.util.HashMap;
import java.util.Map;
import java.util.function.Function;

import org.springframework.beans.factory.annotation.Value;
import org.springframework.security.core.userdetails.UserDetails;
import org.springframework.stereotype.Component;

import io.jsonwebtoken.Claims;
import io.jsonwebtoken.Jwts;
import io.jsonwebtoken.SignatureAlgorithm;

@Component
public class JwtTokenUtil implements Serializable {

    private static final long serialVersionUID = -2550185165626007488L;
    
    public static final long JWT_TOKEN_VALIDITY = 5*60*60;

    @Value("${jwt.secret}")
    private String secret;

    public String getUsernameFromToken(String token) {
        return getClaimFromToken(token, Claims::getSubject);
    }

    public Date getIssuedAtDateFromToken(String token) {
        return getClaimFromToken(token, Claims::getIssuedAt);
    }

    public Date getExpirationDateFromToken(String token) {
        return getClaimFromToken(token, Claims::getExpiration);
    }

    public <T> T getClaimFromToken(String token, Function<Claims, T> claimsResolver) {
        final Claims claims = getAllClaimsFromToken(token);
        return claimsResolver.apply(claims);
    }

    private Claims getAllClaimsFromToken(String token) {
        String encodedString = Base64.getEncoder().encodeToString(secret.getBytes());
        return Jwts.parser().setSigningKey(encodedString).parseClaimsJws(token).getBody();
    }

    private Boolean isTokenExpired(String token) {
        final Date expiration = getExpirationDateFromToken(token);
        return expiration.before(new Date());
    }

    private Boolean ignoreTokenExpiration(String token) {
        // here you specify tokens, for that the expiration is ignored
        return false;
    }

    public String generateToken(UserDetails userDetails) {
        Map<String, Object> claims = new HashMap<>();
        return doGenerateToken(claims, userDetails.getUsername());
    }

    private String doGenerateToken(Map<String, Object> claims, String subject) {
        
        String encodedString = Base64.getEncoder().encodeToString(secret.getBytes());
        return Jwts.builder().setClaims(claims).setSubject(subject).setIssuedAt(new Date(System.currentTimeMillis()))
                .setExpiration(new Date(System.currentTimeMillis() + JWT_TOKEN_VALIDITY*1000)).signWith(SignatureAlgorithm.HS512, encodedString).compact();
    }
    
    public Boolean canTokenBeRefreshed(String token) {
        return (!isTokenExpired(token) || ignoreTokenExpiration(token));
    }

    public Boolean validateToken(String token, UserDetails userDetails) {
        final String username = getUsernameFromToken(token);
        return (username.equals(userDetails.getUsername()) && !isTokenExpired(token));
    }
}