Problem:

There were too many requests from your network. Retry later or contact your administrator if this is an error.


Solution:
Run the following command NextCloud Server as root user

If nextcloud is been installed through ‘snap’
nextcloud.occ security:bruteforce:reset 84.173.231.40


If NextCloud is been installed natively, move to the directory where nextcloud is been installed and run
sudo -u nextcloud occ security:bruteforce:reset 84.173.231.40


Note:
The IP above should be the Internet IP of your device which is actually the IP seen by the server and belongs to your internet provider.

You can us the following URL to find out which IP you have:
https://myip.itmatrix.eu