I've had this problem twice (and forgot the solution as well). I thought I would post the answer for next time I have the same 🙂
It is to do with the deployment server, so when you setup the deploy poll functionality:
splunk set deploy-poll <host>:<port>
Make sure the port is the management port on the server (default is 8089) not the receiver listening port (default 9997). Check this in $SPLUNK_HOME/etc/system/local/deployment-client.conf.
The forwarder still goes to 9997 (or whatever the port you have set the receiver to):
splunk add forward-server <host>:<port> -auth <username>:<password>
This fixes it for me so I hope it helps.
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