getData: function() {
        return {
            'method': this.item.method,
            'additional_data': {
                'yourtextArea': $('#your_text_area_id').val()
            }
        };
    }

<?xml version="1.0" encoding="UTF-8"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Event/etc/events.xsd">
    <event name="sales_order_payment_save_before">
        <observer name="save_bank_infos" instance="IbnabBankInfoObserverSaveBankInfoToOrderObserver"/>
    </event>
</config>

<?php

namespace YourCompanyModuleNameObserver;

use MagentoFrameworkEventObserver as EventObserver;
use MagentoFrameworkEventObserverInterface;
use IbnabBankInfoModelBanktransfer;

/**
 * Class SaveDeliveryDateToOrderObserver
 * @package OyeDeliverydateModelObserver
 */
class SaveBankInfoToOrderObserver implements ObserverInterface {

    protected $_inputParamsResolver;
    protected $_quoteRepository;
    protected $logger;

    /**
     * @param MagentoFrameworkObjectManagerInterface $objectmanager
     */
    public function __construct(MagentoWebapiControllerRestInputParamsResolver $inputParamsResolver, MagentoQuoteModelQuoteRepository $quoteRepository, PsrLogLoggerInterface $logger) {
        $this->_inputParamsResolver = $inputParamsResolver;
        $this->_quoteRepository = $quoteRepository;
        $this->logger = $logger;
    }

    /**
     * @param EventObserver $observer
     * @return $this
     */
    public function execute(EventObserver $observer) {
        $inputParams = $this->_inputParamsResolver->resolve();

        foreach ($inputParams as $inputParam) {
            if ($inputParam instanceof MagentoQuoteModelQuotePayment) {
                $paymentData = $inputParam->getData('additional_data');
                $paymentOrder = $observer->getEvent()->getPayment();
                $order = $paymentOrder->getOrder();
                $quote = $this->_quoteRepository->get($order->getQuoteId());
                $paymentQuote = $quote->getPayment();
                $method = $paymentQuote->getMethodInstance()->getCode();
                if ($method == Banktransfer::PAYMENT_METHOD_BANKTRANSFER_CODE) {

                    if(isset($paymentData['yourtextArea'])){
                    $paymentQuote->setData('your_text_area', $paymentData['yourtextArea']);
                    $paymentOrder->setData('your_text_area', $paymentData['yourtextArea']);
                    }
                }
            }
        }



        //return $this;
    }

}