Bill selection disabled under "Payments"

Hi there,
A very important part of the Software does not work at all. Or do I get something wrong? See the explaination below:

CASE1:
I have added 1 Bill into Akaunting.
Now I have transfered Money for for this Invoices.
I create a payment, but I can not select the corresponding Bill, because the Bill dropdown is disabled.
I know the workaround to make the Bill as payed from the Bill menu directly. But this just works for the most simple cases!

CASE2:
I have added 1 Bill into Akaunting.
Now I have transfered 30% prepayment Money for for this Invoices.
I create a payment, but I can not select the corresponding Bill, because the Bill dropdown is disabled.

CASE3:
I have added 2 Bills into Akaunting.
Now I have transfered the Money for both Invoices at once.
I create a payment, but I can not select the corresponding Bill, because the Bill dropdown is disabled.

You should add payments from the show page of that invoice/bill:

https://akaunting.com/docs/user-manual/sales/invoices

Thanks for your hint, I know how to do that. But ONLY this way is inconvenient.
Usually Accounting software needs to support the following way of work.
1. Accountant import a Bank csv file with all the transactions.
2. Accountant opens the payment and bind the payment to the BILL.
In my opionion this workflow is essential for a proper accounting software!
I know this ways is is more difficult to develop. But without this accounting is difficult and easy to make serious mistakes!