This invocable method gets one contact id from the Flow and returns all associated Opps as a collection variable

Invocable Method to look at Opps

public class contactsListAction {
    //this invocable method takes a single contact from Flow from a text variable
    //and returns a list of lists of opportunities associated with that contact.
    //the list of lists is stored as a collection variable in the Flow.
    @InvocableMethod (label = 'SendContactsGet Opps' description = 'returns opps for this contact.')
    //the method will return a List of Lists of Opportunities, and receive a List of Salesforce ids
    public static List<List<Opportunity>> getContactIds (List<ID> ids) {
        //declare a new list of Opps
        List <Opportunity> oppIds = new List <Opportunity> ();
        //declare a new list of lists of opps
        List<List<Opportunity>> itemListList = new List<List<Opportunity>>();
        //look up the opportunities
        List<Opportunity> opps = [SELECT id,CloseDate,Amount
                                  FROM Opportunity 
                                  WHERE npsp__Primary_Contact__c in :ids AND StageName = 'Closed Won' 
                                  AND CloseDate = THIS_YEAR]; 
        //add each opp to the List
        for (Opportunity opp : opps){
            oppIds.add(opp);
            
        } 
        //add the list to the list of lists
        itemListList.add(oppIds);
        // send list of lists to the Flow	
        return itemListList;
        
    }
    
}