Strange behavior of transcations

I am working on node-postgres and there is a strange transactions.
The function aims at locking user's wallet until the refund process is
complete, then will update item's has_refund to true.
The problem I am facing is the program return no error, but the database is
not updated. Unless I spam the function for multiple times then the value
is updated.
If I remove begin and commit, then the function work perfectly.
const refundService = (itemId) =>{
    await pgPool.query('BEGIN;');
    const users = (await pgPool.query('SELECT * from app_user where
$1=ANY(purchase_list);', [ itemId ])).rows;
    for(let i = 0; i < users.length; i++){
        refund(users[i])
    }
    await pgPool.query('UPDATE item_lists SET has_refund = $1 where id =
$2;', [true,  itemId ]);
    await pgPool.query('COMMIT;');
}

const refund = (user) =>{
    const refund = 10
    await pgPool.query('UPDATE app_user SET wallet = wallet + $1', [refund
]);
}