feat: update refund issues

backend/app/models/users.go

@@ -492,3 +492,21 @@ func (m *usersModel) SetBalance(ctx context.Context, id int64, balance int64) er
 	}
 	return nil
 }
+
+// AddBalance adds the given amount to the user's balance
+func (m *usersModel) AddBalance(ctx context.Context, id int64, amount int64) error {
+	tbl := table.Users
+	stmt := tbl.
+		UPDATE(tbl.Balance).
+		SET(tbl.Balance.ADD(Int64(amount))).
+		WHERE(
+			tbl.ID.EQ(Int64(id)),
+		)
+	m.log.Infof("sql: %s", stmt.DebugSql())
+
+	if _, err := stmt.ExecContext(ctx, db); err != nil {
+		m.log.Errorf("error updating user balance: %v", err)
+		return err
+	}
+	return nil
+}