Payment plugin - POST data from invoice.

I am making payment plugin for Shopware 5.2+ and i have questions about data POST from invoice.
In my plugin I am using direct action in controller to redirect to invoice. Then invoice site after completing payment is using callback to sent POST data to callbackUrl(my callbackAction in controller) and it is redirecting to succesUrl to my returnAction.
Redirecting to returnAction is okay but there is problem with callback because callback can’t get through to my callbackAction coz of 400 BadRequest error. 

I tried using Orders API, to get my post data, but there is authentication, where is needed to have user and password. I dont want to ask people using my plugin to make user with enable api.

Is there any other way to get my post data for controller? 

In Example Payment Plugin I saw using this->request to get status or other elements, but in my plugin it doesnt get any data. 

It is possible that I didn’t see something important and i want to ask for every possible answer, which can help me with this problem. 

Thank You and i am looking forward for every response.