HTTP Error 429: Too Many Requests

I 'm trying to implement slack add-on. Every time logging below "429 Too Many requests " in "_internal" index. I don't know this is cause, but I cannot get all channels messages (Only some messages). Does someone know this issue solution? 11-27-2019 16:25:58.865 +0900 ERROR ExecProcessor - message from "python /opt/splunk/etc/apps/TA-slack/bin/slack_messages.py" HTTP Error 429: Too Many Requests host = splunk01source = /opt/splunk/var/log/splunk/splunkd.logsourcetype = splunkd