403 when using on Siteground, authz_core:error client denied by server config…

Hi, recently found this plugin and love it, so I’m trying to get it installed everywhere I can. My Siteground hosting account doesn’t have any webp extensions enabled and won’t enable them so I’ve set up a remote webp cloud convert instance (composer version, running on linode). That’s tested and confirmed to be working, but I can’t connect to that from Siteground either (with an exact clone of the same WordPress site, so I know there isn’t any conflict of plugins or code specific to my website)
It’s clear to me this problem is specific to Siteground and I have reached out to them for insight, but I figured I’d try here as well.
The error that my Siteground server throws when failing is:
“… [authz_core:error] … client denied by server configuration: … /plugins/webp-express/test/test-run.php”
My theory is there’s something being miscommunicated in the wp-content/.htaccess file that webp express generates. Any theories, anything I could test, any more info needed, please let me know.