If I post this page Help my bike has been stolen to a Facebook or Twitter page, the preview comes up as a 404. Does anyone have any idea why, or know how to fix it please?
Yes I would definitely check these in the FB and Twitter Card Deve tools, but having a quick look at your page source it doesn’t look like you have added data for Twitter Card or Facebook OpenGraph. If you are using Blocs 4 that is a tick box option but it can also be added manually in Blocs 3 using code. These would likely help your presentation and could be checked with the dev tools.
Thanks Flashman and Malachiman. Will take a look.