What to do in case I am getting Rest API error?

HI,
I updated my http request code but now I am getting an error "You are running an old version of the app. Please upgrade to the latest version".
here is my code of calling access token:-

public string getAccessTokenNew(){
String strEndpointUrl='';
HttpRequest tokenRequest = new HttpRequest();
if(objZoomtechConfig !=null){
strEndpointUrl = objZoomtechConfig.RV_Login_URL__c;
tokenRequest.setBody('grant_type=password&client_id=zoom-dev1-client&session_reset=no&username='+objZoomtechConfig.RV_Username__c + '&password='+ objZoomtechConfig.RV_Password__c);
}
//Creating Http request object

tokenRequest.setendpoint(strEndpointUrl);
tokenRequest.setHeader('Content-Type', 'application/x-www-form-urlencoded');
tokenRequest.setmethod('POST');
Http objHttp = new Http();
HttpResponse res = objHttp.send(tokenRequest);  // here response is [Status=OK, StatusCode=200]
system.debug('@@'+res.getBody()); // but here i am getting this  DEBUG |@@ {"response":null,"status":"FAILURE","errorMessage":"You are running an old version of the app. Please upgrade to the latest version."}
objResponse = (responseClass)JSON.deserialize( res.getBody(),responseClass.Class);

if(objResponse.response != NULL){
strAccessToken = objResponse.response.access_token;
system.debug('@@@'+strAccessToken);
objZoomtechConfig.Access_Token__c = objResponse.response.access_token;
objZoomtechConfig.Expires_In__c= Decimal.valueOf(objResponse.response.expires_in);
objZoomtechConfig.Token_Generation_Time__c = System.now();
update objZoomtechConfig;
}

Please guide me, why i am getting this issue?

thanks,
Rahul Kumar