The page build failed. Problem: seo tag

[ghost]

Hello, I installed the theme and GitHub sends me notifications for errors:
Github sent me this email:

The page build failed for the pages branch with the following error:

The tag seo on line 16 in /_layouts/default.html is not a recognized Liquid tag. For more information, see https://docs.github.com/github/working-with-github-pages/troubleshooting-jekyll-build-errors-for-github-pages-sites#unknown-tag-error.

For information on troubleshooting Jekyll see:

https://docs.github.com/articles/troubleshooting-jekyll-builds

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.