Deploy previews not working

Hi Netlify support

I have enabled deploy previews for one of our sites but it is not working in that it is not triggering a
preview build for any pull requests. As we have this site configured to build from webhooks only Im guessing this is the reason? Is it possible to have the site configured to build from webhooks only for the production branch but also allow deploy previews?

Site where its not working - peaceful-wiles-97aae8

Thanks