OK - I've just called eBay customer service with the question and I was passed to a 2nd level CS agent who was extremely helpful so I am passing on all info on here so it can help others.
If you are selling gold or silver (or I expect other valuable metals like platinum) jewellery/items, you NEED to list them under a category that states gold or silver - in my case, I had chosen Vintage jewellery because this is the way I used to sell my vintage items but nowadays, I would need to sell them under Fine jewellery, making sure the category states gold or silver - in that case, you are given the option to opt out of Simple Delivery and choose your own (in my case Special Delivery with RM as I have had problems with EVRI recently).
So for now, I will have to cancel the orders and relist the items so that my buyer can buy them safely and I can send them with insurance.
Hope this helps others - in any doubt, request a call back from eBay CS, they are very helpful I found.
I also mentioned that eBay should try to enhance the AI system by issuing a warning if one tries to list an item with 'gold' or 'silver' in the title but under a category that doesn't reflect the valuable metal.
Anyway, I hope this helps.
Have a lovely day everyone!
