JWT is not well formed

Question

Again my first time developing an asp.net core rest API. See below snippet:

 

 

 

And below is the error:

 

"errorMessage": "System.ArgumentException: IDX12709: CanReadToken() returned false. JWT is not well formed: 'System.String'.\nThe token needs to be in JWS or JWE Compact Serialization Format. (JWS): 'EncodedHeader.EndcodedPayload.EncodedSignature'. (JWE): 'EncodedProtectedHeader.EncodedEncryptedKey.EncodedInitializationVector.EncodedCiphertext.EncodedAuthenticationTag'.\r\n   at System.IdentityModel.Tokens.Jwt.JwtSecurityTokenHandler.ReadJwtToken(String token)\r\n   at System.IdentityModel.Tokens.Jwt.JwtSecurityTokenHandler.ValidateSignature(String token, TokenValidationParameters validationParameters)\r\n   at System.IdentityModel.Tokens.Jwt.JwtSecurityTokenHandler.

Below also is my entire TokenManager:

 

public class TokenManager : ITokenManager
    {
        //private List<Token> listTokens;
        private JwtSecurityTokenHandler tokenHandler;
        private byte[] secretKey;
        public TokenManager()
        {
            tokenHandler = new JwtSecurityTokenHandler();
            secretKey = Encoding.ASCII.GetBytes("xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx");
            //listTokens = new List<Token>();
        }
        public bool Authenticate(string userName, string password)
        {
            if (!string.IsNullOrEmpty(userName) &&
                !string.IsNullOrEmpty(password) &&
                userName.ToLower() == "ltcadmin" &&
                password == "ltcpassword")
                return true;
            else
                return false;
        }

        public string NewToken()
        {
            var tokenDescriptor = new SecurityTokenDescriptor
            {
                Subject = new ClaimsIdentity(new Claim[] { new Claim(ClaimTypes.Name, "LTC LMM") }),
                Expires = DateTime.UtcNow.AddMinutes(5),
                SigningCredentials = new SigningCredentials(
                    new SymmetricSecurityKey(secretKey),
                    SecurityAlgorithms.HmacSha256Signature)
            };

            var token = tokenHandler.CreateToken(tokenDescriptor);
            var jwtString = tokenHandler.WriteToken(token);
            return jwtString;

        }

        public ClaimsPrincipal VerifyToken(string token)
        {
            var claims = tokenHandler.ValidateToken(token,
                new TokenValidationParameters
                {
                    ValidateIssuerSigningKey = true,
                    IssuerSigningKey = new SymmetricSecurityKey(secretKey),
                    ValidateLifetime = true,
                    ValidateAudience = false,
                    ValidateIssuer = false,
                    ClockSkew = TimeSpan.Zero
                }, out SecurityToken validatedToken);
            return claims;
        }

 

 

It says that the error is in line 53. Thank you in advance.