I have inherited a C5 site that I am now supporting.

One of the issues I have to fix is 'Access denied' when user gets to the payment form at the end of checking out for a product. The product is a bookable event, and has no charge. It's marked as being available without being logged-in. The url that is denied is checkout/payment/form.

But what is odd is that checkout works fine for other normal products, just not the bookable event.

Any ideas, or where to start debugging this please?