User send too many amount of request in an amount of time.
For WordPress User That Face Error 429:
Step 1: Change Default Login URL
Change your WordPress default login URL.
Step 2: Check HTTPS Internal Links
Check whether your HTTPS internal links are causing the issue.
Step 3: Deactivate All Your WordPress Plugin
Deactivate all your WordPress Plugin for the time being. By doing this, you need to use FTP to access your website and disable all the plugins.
Step 4: Switch To A Default WordPress Theme
This means you need to disable all the customization theme and using the default WordPress Theme. For the info, you might need to use FTP to access it and disable customization themes.
Step 5: Contact NET
Contact NET Support to get more information about the issue.