Firstly, thanks SO much for replying to me. I really appreciate it
I’ve tried clearing both the session and normal cache (the session table was empty already when I got to it) and that didn’t work.
I didn’t realise there was a diagnostics extension! However, it’s unavailable on that extension page. I’ll have to contact the developer.
I’ll let you know what goes on.
Additionally, I tried adding to the cart via address (can’t remember the link but it ended in the id and quantity) and that did the same.
Is the problem site.
On another site though, it would be:
Notice the additional commas before ‘product’. This is the same on 3 other sites.
I’ll let you know if I can get that diagnostics thing installed.