Cron does not work in pro

I purchased the pro version. Featured images work well when I generate it manually. But cron does not generate any images for Feedwordpress posts. I tried changing the update duration; even then it does not work. I tried this with Google scrapping. I got a warning saying that image generation may be disabled if I try too frequently from Unsplash….so I thought that it is not safe to go with Unsplash if I need frequent generation. Can you please help…how to make this work with Google scrapping.