fix: issue in sales invoices and bills.

server/src/models/Contact.js

@@ -16,6 +16,20 @@ export default class Contact extends TenantModel {
     return ['createdAt', 'updatedAt'];
   }
 
+  /**
+   * Defined virtual attributes.
+   */
+  static get virtualAttributes() {
+    return ['closingBalance'];
+  }
+
+  /**
+   * Closing balance attribute.
+   */
+  closingBalance() {
+    return this.openingBalance + this.balance;
+  }
+
   /**
    * Model modifiers.
    */