Featured images won't display on WP Multisite main site

Hello –

Feedzy is working nicely on a single WP site that I manage but isn’t displaying featured images on the main site of a WP Multisite. I use RSS feeds to display recent post excerpts from several blogs on the main Home page. However, I may have done something dumb to compound the issue.

In reading the support threads, I inserted this into the functions.php file:

add_filter( ‘the_excerpt_rss’, ‘feedzy_insert_thumbnail_RSS’ );
add_filter( ‘the_content_feed’, ‘feedzy_insert_thumbnail_RSS’ );

Which resulted in this error:

Warning: call_user_func_array() expects parameter 1 to be a valid callback, function ‘feedzy_insert_thumbnail_RSS’ not found or invalid function name in /home/content/66/10602266/html/wp-includes/plugin.php

This error message is displaying in place of the excerpts on an internal test site as well as the existing feeds on the main site.

I’ve removed the lines from the PHP file but understand it will take time to clear. Is this correct?

Meantime, what do I need to do to get post featured images to show in the Feedzy feeds?

Thank you!

https://wordpress.org/plugins/feedzy-rss-feeds/