error-RankMath\Replace_Variables\Post_Variables->get_excerpt(

Hello @elearnnow

Thank you for contacting the support and sorry for any inconvenience that might have been caused due to that.

It seems like new tables are not getting created in the Database or some old plugin has left an incorrect entry.

Please follow these steps to fix the issue:

1. Take a complete backup of your website
2. Install this plugin: https://ww.wp.xz.cn/plugins/code-snippets/
3. Head over to the Snippets menu in the left sidebar and click Add New: https://i.rankmath.com/YucUZS
4. Give that post any name and copy the below code in the Code field

add_action(
	'init',
	function() {
		delete_option( 'schema-ActionScheduler_StoreSchema' );
	},
);

5. Select ‘Only run in administration area’ option and click the Save and Activate button: https://i.rankmath.com/D9iOGH
6. Open WordPress Dashboard in a new window
7. Then deactivate recently created snippet from here: https://i.rankmath.com/1k8KcX
8. Then activate the Rank Math plugin again
9. You can disable the Code Snippets plugin if you are not using it

Here’s a video screencast:
https://i.rankmath.com/79gPbv

Please clear all the cache, including the server after following the above process.

That should resolve the issue.