I installed JoomSocial 4.7.8 and wanted to upgrade to Joomla 4.0.3. This update failed. After restoring the backup I can't open the configuration sites in Joomla. I get an error message like: Class 'JFormFieldList' not found or Call to a member function order() on null
My ISP has no clue what this could be. I copied the files from a new 3.10.2 version without success. If I open the database all tables are there and accessible.
What can I do to solve this problem?
Thanks in advance,
Juergen

    htmanager
    Hi
    Migration is important step in Joomla as if any of extension not ready on your site it can break the site.
    I suggest you to restore the site backup and follow the steps as given here : https://www.joomlart.com/blog/joomla-templates/how-to-migrate-joomla-3-to-joomla-4-step-by-step-tutorial
    On current submit URL it appear still using Joomla 3.x

    Disable all extensions and templates that not ready for Joomla 4 before upgrade and try update on staging site first.

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