You are unable to join an online match and you receive the error code 2306-0520.
Restart the Nintendo Switch console.
Hold the POWER Button down for three seconds, and then select "Power Options" followed by "Restart."
Manually enter an alternate DNS.
If the DNS you are attempting to use is not working, entering an alternate DNS may resolve this issue.
Power cycle your home network.
Restarting your network devices may resolve this issue if it is related to the devices being unresponsive.
Situation Not Resolved:
If you would like further assistance with the Nintendo Switch console, please contact Nintendo Customer Service.