Haproxy redis communication problem

Hi Dear forume
I am checking Redis high availability solution via configuration of master and slave Redis Kubernetes pods and sentinel on top of it. For failover of external client connections, I installed haproxy pod. I encountered with some issue while started testing the configuration:

Redis is closing forwarding connections from HAPROXY - client reporting error

Error: Server closed the connection.

BTW: if Redis is configured with an empty password, the connection is passing OK.

I appreciate any idea and advice.
My HA proxy cfg file has the following entries:

maxconn 500

mode http
timeout connect 5000ms
timeout client 50000ms
timeout server 50000ms

frontend rotatingproxies
bind *:3000
default_backend rotateproxy
option http_proxy
option http-use-proxy-header

backend rotateproxy
option http_proxy
server proxyserver user:pass@domain.com:9999
server proxyserver user:pass@domain.com:9999
balance roundrobin