Installing Grow code on Elementor site

Hey everyone, 

I'm trying to set up Grow on my Elementor - Wordpress site. I've read that I can't use the plugin, so I used the manual code instead. When I install it and I check the ‘Check Grow connectivity’ button, it shows that it's connected for 2 seconds, before it turns into ‘There is a problem with your connectivity'. 

Out of all plugins that can cause errors, I only have SG Speed Optimizer, but the ‘Combine Javascript’ future is already turned off. There's also no other plugins bothering. I've cleared my cache, regenerated all CSS files multiple times, but nothing seems to work. 

Curious what else can be the problem!