Could not install the Site Import extension

Tried to install the Site Import extension on Plesk Obsidian v18.0.29_build1800200825.21 os_Ubuntu 18.04
(also failed while on v18.0.28)

This is the error message, looks like it has something to do with dependencies:

Could not install the Site Import extension - Failed

• The execution of post-install.php has failed with the following message:
• [2020-09-01 11:44:24.660] ERR [panel] Execution plesk-migrator-post-install-packages.sh has failed with exit code 1, stdout...

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Could not install the Site Import extension