The query I am using for fetching sales invoice details is as follows SELECT 

    am.id as x_invoice_id,

    am.name AS x_invoice_number,                    -- Order number (Sale order name)

    'InternalUniqueNumber' AS x_order_id,           -- Internal Unique number

    so.name AS x_order_number,                      -- Order title

    am.invoice_date AS x_invoice_date,              -- Order date

    am.amount_untaxed AS x_amount_without_tax,      -- Total excluding tax

    am.amount_total AS x_total_amount,              -- Total including tax

    am.amount_tax AS x_total_tax,                   -- Total VAT (tax amount)

    CASE

        WHEN am.payment_state = 'paid' THEN 'Paid'

        ELSE 'Not Paid'

    END AS x_paid_status,                           -- Paid status

    am.payment_reference AS x_payment_reference,    -- Payment reference

    am.company_id AS x_company_id,                  -- Company ID

    ap.write_date

FROM

    account_move am

JOIN

    sale_order so ON substring(am.invoice_origin FROM 1 FOR 12) = so.name

LEFT JOIN

   account_payment ap on am.id=ap.move_id

WHERE

    am.write_date >= NOW() - INTERVAL '365 days'     -- Check if write_date is within the last 30 days

ORDER BY

    am.id DESC;

Here in this case, I am getting null ap.write_date even if the invoice is paid.

What could be the issue ? Or The way I am fetching the data is wrong? 

Any suggestion will be appreciated.