Bugfix/account cash balance calculation for SELL activities with fees (#6862)

* Fix account cash balance calculation for SELL activities with fees

* Update changelog

CHANGELOG.md

@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
 
+- Resolved an issue with the cash balance calculation of an account for `SELL` activities to ensure fees are correctly subtracted
 - Resolved an exception in the portfolio details endpoint when an asset profile is unmatched
 
 ## 3.3.0 - 2026-05-14

apps/api/src/app/activities/activities.service.ts

@@ -214,19 +214,18 @@ export class ActivitiesService {
     });
 
     if (updateAccountBalance === true) {
-      let amount = new Big(data.unitPrice)
+      let amount = new Big(data.unitPrice).mul(data.quantity);
-        .mul(data.quantity)
-        .plus(data.fee)
-        .toNumber();
 
       if (['BUY', 'FEE'].includes(data.type)) {
-        amount = new Big(amount).mul(-1).toNumber();
+        amount = amount.mul(-1);
       }
 
+      amount = amount.minus(data.fee);
+
       await this.accountService.updateAccountBalance({
         accountId,
-        amount,
         userId,
+        amount: amount.toNumber(),
         currency: data.SymbolProfile.connectOrCreate.create.currency,
         date: data.date as Date
       });