done it with:
iptables -A INPUT -p udp --dport 9987 -j ACCEPT
but i still get:
2021-11-04 19:53:19.664024|INFO |VirtualServerBase|1 |listening on 0.0.0.0:9987, [::]:9987
ts3@rs-zap494161-1:~/teamspeak3-server_linux_amd64/logs$ cat ts3server_2021-11-04__19_53_19.023798_0.log
2021-11-04 19:53:19.023899|INFO |ServerLibPriv | |TeamSpeak 3 Server 3.13.6 (2021-06-09 10:22:37)
2021-11-04 19:53:19.024050|INFO |ServerLibPriv | |SystemInformation: Linux 4.9.0-16-amd64 #1 SMP Debian 4.9.272-2 (2021-07-19) x86_64 Binary: 64bit
2021-11-04 19:53:19.024088|INFO |ServerLibPriv | |Using hardware aes
2021-11-04 19:53:19.024874|INFO |DatabaseQuery | |dbPlugin name: SQLite3 plugin, Version 3, ©TeamSpeak Systems GmbH
2021-11-04 19:53:19.024908|INFO |DatabaseQuery | |dbPlugin version: 3.11.1
2021-11-04 19:53:19.025255|INFO |DatabaseQuery | |checking database integrity (may take a while)
2021-11-04 19:53:19.085244|WARNING |Accounting | |Unable to open licensekey.dat, falling back to limited functionality
2021-11-04 19:53:19.085643|INFO |Accounting | |Licensing Information
2021-11-04 19:53:19.085689|INFO |Accounting | |licensed to : Anonymous
2021-11-04 19:53:19.085719|INFO |Accounting | |type : No License
2021-11-04 19:53:19.085750|INFO |Accounting | |starting date : Thu Oct 1 00:00:00 2020
2021-11-04 19:53:19.085766|INFO |Accounting | |ending date : Tue Nov 1 00:00:00 2022
2021-11-04 19:53:19.085801|INFO |Accounting | |max virtualservers: 1
2021-11-04 19:53:19.085813|INFO |Accounting | |max slots : 32
2021-11-04 19:53:19.598092|INFO | | |Puzzle precompute time: 486
2021-11-04 19:53:19.598799|INFO |FileManager | |listening on 0.0.0.0:30033, [::]:30033
2021-11-04 19:53:19.609236|INFO |Query | |Using a query thread pool size of 2
2021-11-04 19:53:19.664395|INFO |Query | |listening for query on 0.0.0.0:10011, [::]:10011
2021-11-04 19:53:19.664723|INFO |Query | |listening for ssh query on 0.0.0.0:10022, [::]:10022
2021-11-04 19:53:19.664857|INFO |Query | |listening for http query on 0.0.0.0:10080, [::]:10080
2021-11-04 19:53:19.664951|INFO |CIDRManager | |updated query_ip_allowlist ips: 127.0.0.1/32, ::1/128,
