Amount_mismatch error

When trying a test (PayPal sandbox) purchase using Woocommerce Gift Cards discount, I get this error message: AMOUNT_MISMATCH: Should equal item_total + tax_total + shipping + handling + insurance – shipping_discount – discount.

The totals are displaying correctly in the checkout. All plugins and theme are up to date. Normal (non-discounted) purchases work fine.

Any ideas please?

Thanks in advance.

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