"Variable does not exist" error where variable is a class does exist

Question

I have an Apex class OpportunityUpserter with a static method, where the static method makes a call to another static method in a class called IntegrationUtilities, as shown below. This gives me a compile error in VC Code Variable does not exist: IntegrationUtilities. For some reason, the Apex class IntegrationUtilities is not recognized from insertOpportunities method. I know that static methods can't access instance variables. But in this case, the static method is trying to access another static method in a different class. What could be the reason for this error?

(All the classes were created using the "SFDX: Create Apex Class" option in SF CLI and all classes have a metadata file.)

public with sharing class OpportunityUpserter {   
   @Future(callout=true)   
   public static void upsertOpportunities(Set<Id> opportunityIds, String action) {        
      Opportunity[] opportunitiesToUpsert = [SELECT Id, name, owner.name, servicenow_sys_id__c FROM Opportunity WHERE Id IN :opportunityIds];        
      insertOpportunities(opportunitiesToUpsert);           
   }   

   public static void insertOpportunities(Opportunity[] opportunitiesToInsert) {
      //code to make REST request goes here   
      sys_id = IntegrationUtilities.getFieldsFromResponse(response, action).get('sys_id');   
   }
}

public with sharing class IntegrationUtilities {      
   public static Map<String, String> getFieldsFromResponse(HttpResponse response, String action) {
           // more code here
           // return Map<String, String>     
   }
}

Answer 1

Most probably you have an error inside IntegrationUtilities class and it's not compiled hence cannot be deployed to the org and cannot be referenced by another class.

My advice would be to push/deploy both classes to the org as the separate classes(without calling IntegrationUtilities class methods inside OpportunityUpserter). And check if they can be deployed.