Coupon not generated

Hi there,

Just installed and set up as per video. All looked OK until put in order and no coupon generated. Click on Generate Coupon link (under order in WooCommerce > Orders) and given a HTTP ERROR 500.

Back to orders page and can now see coupon ID with status as Sended (!) but no email received by customer.

Running child of X-theme on WP 4.9.2 and WooCommerce 3.2.6.

Help appreciated.

Dave