I have a custom module on Odoo14,

I have do customization that generate sale sale.order automatically after clicking on my custom button.

But for now, I want to do, if Invoice (from account.move) got paid, I want my all of my items on stock.picking get deliver, which is the Invoice and stock.picking is related on the same sale.order.

So far, I try to make it like this:

class AccountMove(models.Model):
    _inherit = "account.move"

    course_registration_id = fields.Many2one('aqur.course.registration',
                                             string='Course Registration ID', readonly=True, tracking=True,
                                             states={'draft': [('readonly', False)]}, change_default=True)
    course_registration_number = fields.Char(related='course_registration_id.course_registration_number',
                                             string='Course Registration Number')

    def write(self, vals):
        invoice_course = self.env['account.move'].search(
            [('course_registration_id', '!=', False), ('course_registration_number', '!=', False)])

        for rec in invoice_course:
            stock_picking = self.env['stock.picking'].search(
                [('course_registration_id', '=', rec.course_registration_id.id),
                 ('course_registration_number', '=', rec.course_registration_number)])

            if rec.payment_state == 'paid' and stock_picking:
                for mv in stock_picking.move_ids_without_package:
                    mv.quantity_done = mv.product_uom_qty
                stock_picking.button_validate()

        return super(AccountMove, self).write(vals)

But I got this message when I do payment on my invoice:

You cannot validate a transfer if no quantities are reserved nor done. To force the transfer, switch in edit mode and encode the done quantities.

I also do testing to fill the quantity done on stock.picking by manually edit on the form,
but when I do register payment on my invoice, I always got the error.

So, whats wrong in my code?,
please, any help, source or tutorial to do achive that will be very appreaciated.

Thanks,
Tri Nanda