Incorrect token in Salesforce Marketing Cloud (401)

Question

I would like the get the External Key of the Data Extension related to the Journey Builder. From this step, I need to use the REST API integration and WSProxy. Then, to call the REST API, I need to use the token, right?

The sample token that I got: n4Iu4WRSeDEPjkiged6mQg1ddr3dZnPVhiYTukZF1yGRPNUfA06vitpxxxxxxxxxxxxx

Unfortunately, I always get error 401 every time I use such token even I just refresh the token.

I have followed the steps from this link to get token https://ampscript.xyz/tips-and-tricks/how-to-create-store-use-rest-api-tokens-in-sfmc/

I first create the Data Extension named Rest_Tokens

Second, I create the encryption keys

Then, i use this code from the given link to ask for the token.

<script runat='server'>

    Platform.Load('core', '1');

    var config = {
        endpoint: "https://{{ YOUR DOMAIN }}.auth.marketingcloudapis.com/v2/token",
        credentials: {
            "{{ BU ID }}": {
                "grant_type": "client_credentials",
                "client_id": "{{ CLIENT ID }}",
                "client_secret": "{{ CLIENT SECRET }}"
            }
        },
        storage: {
            de: "REST_Tokens",
            name: "DEMO"
        },
        bu: Platform.Function.AuthenticatedMemberID(),
        localDate: DateTime.SystemDateToLocalDate(Now())
    }

    try {

        var auth = retrieveToken();

        Write(Stringify(auth));

    } catch(error) {
        
        Write(Stringify(error));
        
    }

    function requestToken() {

        var request = HTTP.Post(config.endpoint, "application/json", Stringify(config.credentials[config.bu]));

        if (request.StatusCode == 200) {

            var result = Platform.Function.ParseJSON(request.Response[0]);

            var parsedDate = new Date(config.localDate);

            var expirationDate = new Date(parsedDate.getTime() + (result.expires_in * 1000));

            return {
                "token": result.access_token,
                "url": result.rest_instance_url,
                "expires": expirationDate
            }

        } else {
            
            throw "Couldn't request the token. Status: " + request.StatusCode;
        
        }
    }

    function retrieveToken() {

        var request = Platform.Function.LookupRows(config.storage.de, "Name", config.storage.name);

        var result = request[0];

        if(result != null && (new Date(config.localDate) < new Date(result.ExpirationDate))) {

            return {
                "token": decryptSymmetric(result.access_token),
                "url": decryptSymmetric(result.rest_instance_url),
                "expires": result.ExpirationDate
            }

        } else {

            var result = requestToken();

            var upsert = storeToken(result);

            if(upsert > 0) {
                
                return result;
                
            } else {
                
                throw "Token not saved"
                
            }
        }
    }

    function storeToken(result) {

        var rows = Platform.Function.UpsertData(
            config.storage.de,
            ["Name"], [config.storage.name],
            ["access_token", "rest_instance_url", "ExpirationDate"],
            [encryptSymmetric(result.token), encryptSymmetric(result.url), result.expires]
        );

        if(rows > 0) {
            
            return rows; 
            
        } else {
            
            throw "Token storage failed"
            
        }
    }
    
    function decryptSymmetric(str) {

        Variable.SetValue("@ToDecrypt", str)

        var scr = "";
            scr += "\%\%[";
            scr += "SET @Decrypted = DecryptSymmetric(@ToDecrypt, 'AES', 'pwd', @null, 'slt', @null, 'vec', @null)";
            scr += "Output(Concat(@Decrypted))";
            scr += "]\%\%";

        return Platform.Function.TreatAsContent(scr);
    }

    function encryptSymmetric(str) {

        Variable.SetValue("@ToEncrypt", str)

        var scr = "";
            scr += "\%\%[";
            scr += "SET @Encrypted = EncryptSymmetric(@ToEncrypt, 'AES', 'pwd', @null, 'slt', @null, 'vec', @null)";
            scr += "Output(Concat(@Encrypted))";
            scr += "]\%\%";

        return Platform.Function.TreatAsContent(scr);
    }
</script>