The "Association Indication" command always returns the code "0xFF"

I didn’t find information about the DA command in the documentation, can you tell me where I can read about it?

https://www.digi.com/resources/documentation/digidocs/90002273/Default.htm#reference/r_cmd_da.htm?Highlight=DA

Nice information. Thank you. I am a newbie here and need to hear from you more on this topic:)