actionv_server_pos.py

records = env['pos.order'].browse(context.get('active_ids'))
for object in records:
    if not object.amount_total < 0:
        # When is created a new register, verify that partner have VAT, and
        # create and validate automatically the invoice
        object.action_create_invoice()
        # Are related the customer journals with the id of payment method
        # Dict = {journal_id: payment_method_id}
        mapping = {
            37: 3,
            35: 3,
            36: 3,
            31: 4,
            32: 4,
            33: 4,
            34: 3,
            26: 4,
            1: 1,
            2: 1,
            22: 1,
            29: 1,
            30: 1}
        # I make sure that journal exist in the system
        if env['account.journal'].search([('id', 'in', mapping.keys())]):
            # Search in all payments related with the order the movement with
            # more amount to assign like payment method
            statement = env['account.bank.statement.line'].search([('id', 'in', object.statement_ids.ids), ('amount', '>=', 0)], order='amount', limit=1)
            # Write the payment method that are taken from mapping dict
            object.invoice_id.write({'payment_method_id': mapping.get(statement.journal_id.id, False)})
        object.action_validate_invoice()