For internally used SSL-GDPR certificates on a web hosting package with checkdomain, the revalidation is performed automatically. 

You do not need to do anything yourself.

The certificate has a duration of 90 days.

14 days before the end of the validity period you will receive an e-mail with new validation files, which have to be uploaded to the server.

Unzip the attached domain_validation.zip and upload the folders (from .well-known) including the validation files into the main directory of the domain on your server.

Please note that the directories are partially hidden. 
You can recognize this by the fact that the directory begins with a dot (.well-known). As a result, some operating systems do not display these directories by default. You may also need to configure your FTP client to upload hidden directories.

Under Windows

- If you press the [Windows] and [E] keys simultaneously, the "Explorer" opens.

- If you switch to the "View" tab at the top, various options appear.

- Under the category "Show/Hide" you will find the entry "Hidden items".

- If you activate this option, the hidden files are also displayed in the Explorer.

Under Mac OS

Via the "Terminal" you can see all hidden files and folders with a special command. Start the program by pressing 

Enter the keyword "Terminal" in the Spotlight search and select the first hit.

- After starting the terminal, enter the following command: 

defaults write com.apple.finder AppleShowAllFiles 1

- A restart of the system is not necessary. However, a reset is required for the Finder. To do this, enter the following command in the terminal: 

killall Finder

- Now the hidden files and folders appear transparent in your Finder. If you now want to hide all hidden files again, type this command in the terminal: 

defaults write com.apple.finder AppleShowAllFiles 0

- Afterwards you have to restart the Finder in the terminal: 

killall Finder

Make sure that these files are accessible via a call in the browser.

A white page with the validation code must appear when the file is called.

If, for example, a 404 page appears instead when the URL is called, validation by Let´s Encrypt is not possible.

48 hours after receiving the new validation files, Let´s Encrypt starts a final validation attempt. Before this, the system checks every 2 minutes whether the files are stored.

If the validation is successful, you will receive a new certificate by e-mail, which must be reinstalled on the server.

The installation can be carried out directly. If necessary, existing days of the remaining runtime will be taken over.