send-sms-ssjs-api.html

<script runat="server">
Platform.Load("Core","1.1.1");
try {

//API authentication  
var authEndpoint = "";  //provide authentication endpoint
var payload = {
        clientId: "",  //provide Client Id
        clientSecret: ""  //provide Client Secret
    };
var url = authEndpoint + "/v1/requestToken";  
var contentType = "application/json";


   var accessTokenRequest = HTTP.Post(url, contentType, Stringify(payload));
   if(accessTokenRequest.StatusCode == 200) {
        var tokenResponse = Platform.Function.ParseJSON(accessTokenRequest.Response[0]);
        var accessToken = tokenResponse.accessToken;
   }

//make a call using the messageContact route
var headerNames = ["Authorization"];
var headerValues = ["Bearer " + accessToken];
var smsEndpoint = "";  //provide rest endpoint
var smsPayload = {
    "mobileNumbers": [
    ""  //pass phone number
    ],
    "Subscribe": true,
    "Resubscribe": true,
    "keyword": ""  //provide KEYWORD
};
var smsUrl = smsEndpoint + "/sms/v1/messageContact/xxxxxxxxx/send";  //provide message API key
  
var sendSMS = HTTP.Post(smsUrl, contentType, Stringify(smsPayload), headerNames, headerValues);

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

  
</script>

this code is broken in every way, the HTTP.Post doesn't work at all

@rain89146 I just checked and the code works just fine, I even set up a CloudPage with the above code (unfortunately it only works with Polish phone numbers) - https://mcg7y3r488-d6mcg1dym88btc7g4.pub.sfmc-content.com/x1p4cdfw5ud
I suggest you take your code to https://salesforce.stackexchange.com/ and have someone help you fix it there instead of making vicious comments