CraftCMS with Redis: Failed to open redis DB connection (tcp://:, database=): 0 – Failed to parse address ":"

I have yii2 and yii2-redis installed on a CraftCMS project, but when I fire up the project, I get an error message that reads:

Database Exception – yiidbException
Failed to open redis DB connection (tcp://:, database=): 0 – Failed to parse address ":"
Error Info: Failed to parse address ":"

I’m not quite sure what to do with this error. In my .env file, I put in:

REDIS_HOST=localhost
REDIS_PORT=3306
REDIS_PASSWORD=
REDIS_KEY_PREFIX=craft

But that only yielded a different error:

Database Exception – yiidbException
Failed to open redis DB connection (tcp://:3306, database=): 0 – php_network_getaddresses:
getaddrinfo failed: nodename nor servname provided, or not known
Error Info: php_network_getaddresses: getaddrinfo failed: nodename nor servname provided, or not known

Help?

Additional context: I didn’t set up the build for this project, so I more or less inherited this Redis setup.

Update:
I went and dug into the config file for the Redis setup and found a misnaming between the .env variables and what was present in the .env file. Now I’m getting a completely different error:

"Received illegal data from redis: Redis command was: SELECT 0"