Ubuntu 20.04 - Changed "white-list=true" in server.properties. When enter "whitelist on", console returned "Not implemented" but actually it is working.

I faced the problem in the following combination of Bedrock Dedicated Server:

• bedrock-server-1.18.31.04 on Ubuntu Linux 20.04

My Linux user called "mcadmin". Following is the output of the command "ll server.properties".
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mcadmin@SME-pl1:~/minecraft/bedrock_server/bedrock-server-1.18.31.04$ ll server.properties
rw-rw-r- 1 mcadmin mcadmin 5388 May 15 23:06 server.properties
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In the file "server.properties", I edited whitelist parameter as "white-list=ture".
I use the following commend to start the bedrock server.
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mcadmin@SME-pl1:~/minecraft/bedrock_server/bedrock-server-1.18.31.04$ sudo ./bedrock_server
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After server started, I typed the "whitelist on" command but it shows "Not implemented" as follow:
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[2022-05-15 23:06:47:592 INFO] Server started.
[2022-05-15 23:06:47:619 INFO] IPv4 supported, port: 41603
[2022-05-15 23:06:47:619 INFO] IPv6 supported, port: 51601
whitelist on
Not implemented
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However, I found that when I removed the player (let's say XXX) from the whitelist, XXX no longer able to join the server. XXX will see a message prompt "You're not invited to play on this server."

The message "Not implemented" is very confusing. Would you please verify if this is a bug. Thanks.