After you download your theme files, you can delete them from your server

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After that, you need to rename the plugins-old folder to plugins. This will make all previously installed plugins available for WordPress. However, these plugins will remain disabled.

You need to go to the WordPress admin area and then go to the Plugins page. You can activate your plugins one by one and visit different pages of your website after activating each plugin. Keep doing this until you find the plugin that is causing the 503 error.

If this step solves your problem, you do not need to follow the rest of the instructions on this page. Otherwise, you can proceed to the next step.

For more details, see our guide on how to deactivate all list of taiwan cell phone number plugins if you don't have access to wp-admin.
If deactivating plugins doesn't fix the problem, the next step would be to switch to a default WordPress theme . This will deactivate your current WordPress theme.

First, you need to connect to your WordPress website using an FTP client or the file manager in cPanel. Once connected, go to the folder /wp-content/themes/.

Go to the themes folderNext, you can locate your currently active WordPress theme and download it to your computer as a backup.To do this, simply right-click on the folder named after your website theme and click on the “Download” option.