Discount not applied in PayPal transaction

[RobinSomes]

CC6.2.9 / All In One Shipping 1.0.19 /  PayPal Commerce Platform 1.3.20 

Site: shop.robinsomes.co.uk

I've just had a sale this evening, where the customer used a discount code to get 15% off the order. In the shop, the order appears to have processed perfectly:

            Sub-total: £3.50

15.14% discount: -£0.53

                    Total: £2.98

- see the first image attached below.

However, looking at the PayPal transaction, there's no discount amount applied (image in first reply).

Looking at the request log, there are 5 entries in red which look to be the cause of the problem (image in 2nd reply).

Previous discounted orders have gone through OK; I've not knowingly changed anything about the site.

Inevitable question: what do I do to prevent this happening again?

TIA, Robin

2 minutes ago, RobinSomes said:

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