Customize a Shopware 6 payment plugin by adding a pop-up

I am searching for a developer with experience in customization of Shopware 6 plugins. The project is about customizing the payment plugin by Micropayment GmbH (I can't attach it as a .zip file, but it is available for free at the Micropayment website https://www.micropayment.de/products/plugins/shopware6/?lang=en).

When there is a failure with connecting to the Micropayment API, for example because of invalidation of an access key, right now, the plugin just won't show any reaction. I want it to show an error message or pop-up in this event to present a custom message to the customer, e.g. to contact customer support because of failure in payment processing. The message should be customizable, ideally by an additional snippet in the snippet section of the Shopware 6 backend. The changes should be made to the plugin itself, so in case we have to reinstall it the changes won't get lost.

The person who gets awarded this project will get access to a testing environment we prepared (Shopware 6.4.20.0 Admin access, root access to the server).

Please let me know in your messages if you have prior experience in Shopware 6.

If you have experience in Shopware 6 development, I'm looking forward to your offers!