Links to a contribution page with checksum and contact ID generate a fatal error
I would guess that anonymous users are not able to view and use contribution pages.
Confirm and change this at:
Administer-&gt;Users and Permissions-&gt;Permissions (Access Control)-&gt;Wordpress Access Control.
OR
https://yoursite.tld/wp-admin/admin.php?page=CiviCRM&amp;q=civicrm%2Fadmin%2Faccess%2Fwp-permissions&amp;reset=1