Make sure that you have port forwarded ipv4, and are allowing inbound traffic on ipv6, then just set floodfill = true, bandwidth = X, and share = 100 in your /etc/i2pd/i2pd.conf, then just restart and you should be good to go.

You may also need to increase the default open files limit with a service file dropin, the default is already increased, so if it doesnt cause any issues, you dont need to touch it