How did I fix «log.dir invalid, Cannot create file in dir» for RabbitMQ in Debian 10?

To fix the issue, you nee make log.dir writable by RabbitMQ.
In my case, I have:

log.dir = /var/log/_mage2pro/rabbitmq

So I did:

chmod -R -v 777 /var/log/_mage2pro/rabbitmq