certbot and redis tls: which files I need to use?

Question

I'm trying to setup TLS with a self-hosted redis server.

I've installed certbot on my server and ran the following command:

sudo certbot certonly --standalone

This generated the following files:

chain.pem
fullchain.pem
privkey.pem
cert.pem

I followed the information posted here and I edited the following settings in my redis.conf-file:

port 0
tls-port 6379
tls-cert-file /etc/letsencrypt/live/mydomain.com/fullchain.pem
tls-key-file /etc/letsencrypt/live/mydomain.com/privkey.pem
tls-ca-cert-file /etc/letsencrypt/live/mydomain.com/cert.pem

This doesn't work, the redis.service won't restart and gives an error.

I probably have the wrong files in my config. Can someone help me out which certificate-files I need to use?

Edit: when running /usr/bin/redis /etc/redis/redis.conf directly, everything works. Seems there is some problem with the redis.service.