Can’t set rules by product

I’m getting this error in the console:
https://xxxx/wp-admin/admin-ajax.php?action=whsma_product_fees_conditions_values_ajax&condition=product&count=1&_fs_blog_admin=true 500 (Internal Server Error)

It worked okay on my local development environment, and it doesn’t seem to be a plugin conflict as far as I can tell. The other options work fine; I just can’t set rules by product.

Any ideas? I’m afraid I’m not a developer so that’s about as much information as I’ve got for you. I tried both Chrome and Firefox, if that helps.

Thank you!