Trying to debug a theme issue on topic page

I know this is not an issue with Forum WP as I've tested on another theme. I'm hopeful that someone can kindly help me debug the issue:


I've inherited a website with a custom theme and i'm trying to get the forum up and running.
The top page is completely black I have added a custom override template and add some error logging to get some information.

Error log:
[04-Mar-2025 16:17:01 UTC] PHP Fatal error: Uncaught TypeError: Cannot access offset of type string on string in /home/sites/9a/5/5e983df95e/public_html/wp-content/themes/global-leadership-exchange/single-fmwp_topic.php:18
Stack trace:
#0 /home/sites/9a/5/5e983df95e/public_html/wp-includes/template-loader.php(106): include()
#1 /home/sites/9a/5/5e983df95e/public_html/wp-blog-header.php(19): require_once('/home/sites/9a/...')
#2 /home/sites/9a/5/5e983df95e/public_html/index.php(17): require('/home/sites/9a/...')
#3 {main}
thrown in /home/sites/9a/5/5e983df95e/public_html/wp-content/themes/global-leadership-exchange/single-fmwp_topic.php on line 18

Thanks