Modify custom attribute value before place order

Question

I have a custom attribute that is placed in the Billing Address section. Now there's a condition that I only need to save the first 200 character of my custom attribute text box. Is there an event or observer that will intercept this request before proceeding to save/place order? So basically on the checkout page after inputting the text in my custom attribute when user click the Place Order button I want to check this input first if it's beyond the limit then I will trim the text. How do I do this?

Update:

When I tried to intercept the request under Magento\Checkout\Api\GuestPaymentInformationManagementInterface I was able to view the personal_message custom attribute that I'm looking at. But when I try to save or change the value it didn't allow me. How can I override it?

<type name="Magento\Checkout\Api\GuestPaymentInformationManagementInterface">
    <plugin name="validate-billing-information" type="Vendor\Module\Plugin\Checkout\BillingValidation"/>
</type>

And this is the code I was trying to overwrite

public function beforeSavePaymentInformationAndPlaceOrder(
    \Magento\Checkout\Api\GuestPaymentInformationManagementInterface $subject,
        $cartId,
        $email,
        \Magento\Quote\Api\Data\PaymentInterface $paymentMethod,
        \Magento\Quote\Api\Data\AddressInterface $billingAddress = null
) {
   $billingAddress->setPersonalMessage("This is an overwritten message");
   $billingAddress->save();
}

But doing this throws an error of

webapi-5f6f60228b3a3; Message: SQLSTATE[23000]: Integrity constraint violation: 1452 Cannot add or update a child row: a foreign key constraint fails (`homestead_goodgifts`.`quote_address`, CONSTRAINT `QUOTE_ADDRESS_QUOTE_ID_QUOTE_ENTITY_ID` FOREIGN KEY (`quote_id`) REFERENCES 
    

Answer 1

You can observe the sales_order_place_before event.

Here is an example:

namespace [VendorName]\[ModuleName]\Observer;

use Magento\Framework\Event\Observer;
use Magento\Framework\Event\ObserverInterface;
use Magento\Sales\Api\OrderAddressRepositoryInterface;

class [ObserverName] implements ObserverInterface
{
    private $orderAddressRepository;

    public function __construct(OrderAddressRepositoryInterface $orderAddressRepository)
    {
        $this->orderAddressRepository = $orderAddressRepository;
    }

    public function execute(Observer $observer)
    {
        $order = $observer->getEvent()->getOrder();
        $billingAddress = $order->getBillingAddress();
        if ($billingAddress) {
            $[yourCustomAttributeName] = $billingAddress->getCustomAttribute('[your_custom_attribute_name]');
            if (!empty($[yourCustomAttributeName]) && count($[yourCustomAttributeName]) > 200) {
                $[yourCustomAttributeName] = substr($[yourCustomAttributeName], 0, 200);
                $billingAddress->setCustomAttribute('your_custom_attribute_name', $[yourCustomAttributeName]);
                $this->orderAddressRepository->save($billingAddress);
            }
        }
    }

}

[updated answer]

Try observing the checkout_submit_before.

namespace [VendorName]\[ModuleName]\Observer;

use Magento\Framework\Event\Observer;
use Magento\Framework\Event\ObserverInterface;

class [ObserverName] implements ObserverInterface
{
    public function execute(Observer $observer)
    {
        $quote = $observer->getEvent()->getQuote();
        $billingAddress = $quote->getBillingAddress();
        if ($billingAddress) {
            $personalMessage = $billingAddress->getCustomAttribute('personal_message');
            if (!empty($personalMessage) && count($personalMessage) > 200) {
                $personalMessage = substr($personalMessage, 0, 200);
                $billingAddress->setCustomAttribute('personal_message', $personalMessage);
            }
        }
    }

}