Theme causing error

Hi there, I am using the siteground optimized plugin. The error "could not connect to the WordPress rest API"comes up, see image attached. I do have a security plugin and I have checked that, that doesn't cause conflict either. The theme Kuteshop is causing this error DEFINITELY. I have contacted my hosting provider (siteground) and they have told me to ask you, the developer. I know it is the theme for DEFINITE as I switched to the default theme and plugin started working. Please fix this issue ASAP. VERY IMPORTANT. Thanks.