I've got a trigger that should just sum up the number of child records on a field in the parent.

Trigger below compiles but the aggregattion in the map doesn't seem to be working right.  Basically what should happen is that, anytime there is an account record  x of record type partner, any customer usage records created from accounts where the referrring partner is x should update the account field Active_Paying_M__c with that new add.

Example:

Partner = x

Sales account where referring partner is x = y 

Sales account where referring partner is x = r

customer usage record on y = z

customer usage record on r = p

If the above are true, the field value in Active_Paying_M__c on record x should be "2".  Trigger below keeps setting the value to 1 in testing.

Any ideas?  I suspect the issue is with the first map but not sure

trigger CustomerUsage on Customer_Usage__c (before insert, before update, after insert, after update, after delete) {

// ------------------------------------------------------
//test
// ------------------------------------------------------

if ((Trigger.isInsert || Trigger.isUpdate) && Trigger.isAfter) {    
     
set<Id> AccountIds = new set<Id>();
 
  if(trigger.isInsert || trigger.isUpdate){
    for(Customer_Usage__c p : trigger.new){
      AccountIds.add(p.Account__c);
    }
  }
 
  map<Id,Double> AccountMap = new map <Id,Double>();
 
  for(AggregateResult  q : [select Account__c,sum(FPID_Value__c)
    from Customer_Usage__c where Account__c IN :AccountIds group by Account__c ]){
      AccountMap.put(
      
      (ID)q.get('Account__c'),
      (Double)q.get('expr0')
      
      
      );
  }
 
//stage 1 - find the lookup records id's
List<String> tempLst=new List<String>();
Map<String, String> accountid_partner_map=new Map<String, String>();

for(Account a : [Select Id, Referring_Partner__c
        from Account
        where Id IN :AccountIds]){
    tempLst.add(a.Referring_Partner__c);
    accountid_partner_map.put(a.Referring_Partner__c, a.id);
}

//stage 2 - retreive the lookup records + update their dates.
List <Account> AccountsToUpdate = new List <Account>();
 
  for(Account a : [Select Id,Referring_Partner__c,Partner_Most_Recent_Gross_Add__c from Account where Id IN :tempLst]){
    Double FPID = AccountMap.get(accountid_partner_map.get(a.Id));
     
     a.Active_Paying_M__c = FPID ;
     
     
    
     AccountsToUpdate.add(a);
 
  update AccountsToUpdate;
 
  }
  
}
}