如何将其他信息添加到php数组中

I use this php code:

public function checkout(&$order, &$response)
    {
        $settings = Settings::get($order->seller_id);
        $readon= 'maksājums'; 
        $readon= $order->id;
        $order->custom([
            'payment_details' => [
                'bank_name' => [ 'label' => $this->_->_('Bank Name'), 'value' => $settings->bank_name ],
                'account_owner' => [ 'label' => $this->_->_('Account Owner'), 'value' => $settings->account_owner ],
                //'bic' => [ 'label' => $this->_->_('BIC/SWIFT'), 'value' => $settings->bic ],
                'iban' => ['label' => $this->_->_('IBAN'), 'value' => $settings->iban ],
                'reason' => [ 'label' => $this->_->_('Reason for Payment'), 'value' => $readon],
            ],
        ]);

        $response = [];
        $response['redirect'] = $this->meta('manual_url');

        return Payment::STATUS_OK;
    }

Problem is that I want to add additional text on value readon. Right now $readon show only order number, but I want that it display text like "Please make payment for Order No.$order->id"

Just concatenate the string with what you need. Like this,

$readon= "Please make payment for Order No. ".$order->id;