How is APS layer security implemented in XBee?

I am working on the project which involves receiving data by XBee module as coordinator from 3rd party device as end device. Specification ZigBee 2006 is used. Encryption is enabled on the APS layer only.
How can I configure XBee module to enforce using only APS layer encryption (not NWK)?

Product family: XB24C
Firmware version: 0x4059

For that product you you option bit 3 for that function.

If I omit this procedure should received data (event with encrypted APS) still arrive in UART?

That would be dependent upon where the encryption is being done. If it is being done outside of the radios in your application, then yes you would still receive it. Otherwise you may not.

What is the proper configuration for this purpose? How can I enable only APS layer encryption without NWK layer encryption?
Because I tried to use EE = 0x01, EO = 0x08 and KY = “some key” and transmitted packets become encrypted on both layers.

Sorry that would be an option bit of 20 instead of 0x80. Just understand that you will most likely still have some sort of network level encryption as well.

You will need to also use both a network key and KY value as well. By doing this, it should encrypt the data on a per packet basis.

I made a typo. I meant 0x8, not 0x80 (clearly that it is bit 3). But why 20? Is this dec or hex? And what does it mean?

The 0x20 is a Hex value that needs to be set in the EO command. This in addition to the above settings that you will need to set.

As was clarified later, APS layer encryption can only be used together with NWK layer encryption.