Cannot install Acronis Backup Extension in Plesk on Debian 10: "Failed to install package "linux-headers-4.19.0-16-cloud-amd64"

Symptoms

• Plesk is installed on Debian 10
• Cannot use Acronis Backup extension, the following error is shown in Plesk UI upon accessing the extension:

PLESK_ERROR: "Failed to install package "linux-headers-4.19.0-16-cloud-amd64". Please try to install it manually and then restart the backup agent installation."

Cause

Kernel was updated, but server was not rebooted yet, therefore, apt-get installed outdated version of linux-headers-$(uname -r) package

Resolution

1. Reboot the server to make sure that system kernel is updated to the latest version.
2. Try to install Acronis after that again:
   https://support.plesk.com/hc/en-us/articles/12377511962007-How-to-manage-Plesk-extensions-install-disable-remove-update