Is it possible to connect this accounting software to bank system Postbank https://www.postbank.de/? This possibility could bring the significant assistance in our work.

Hello, usera-kravchenko.

I hope you're doing well. Being efficient in this line of work would definitely save time, so I'd like to give some details about the supportability of Postbank. 

It looks like Postbank isn't participating for our Online Banking connection. So we're unable to connect it with QuickBooks. However, we can send a request to Postbank and have them participate as one of our supported bank. Here's how to do it: 

1. Go to Banking, then click the Connect account button.
2. Enter www.postbank.de on the search box to bring up the request form.
3. Enter the Account provider name and the sign-in URL.
4. Proceed with Request. 

I should also mention that the bank has the final say on the participation request. 

In the meantime, we can manually upload your Postbank transactions to QuickBooks Online using an Excel file. This way, we'll be able to work on your transactions and categorize them for your books. 

We can take a look at this article for more details: Manually upload transactions into QuickBooks Online. 

After getting your transactions in to QuickBooks Online manually, we can start categorizing them for your books. 

In case you need to reconcile your transactions in the future, I have just the article to help you out: Reconcile an account in QuickBooks Online. 
 

I'd be glad to help you out in the near future again regarding the Online Bank connection, your transactions, and any other areas in QuickBooks. Just reply here and I'll get back to you.