Paypal IPN issue

Built a site for a customer on GoDaddy hosting. Did it the same as I do all my sites with woocommerce. When an order is placed and paid for with Paypal it updates correctly the order status to processing, but stock qty doesn’t reduce.

I tried it with COD and it worked fine, stock reduced as it should.

I have set up Paypal API authorization and checked that email is correct and the same.
I have tried it with no plugins (except woocommerce) and default theme. No change.

Called GoDaddy twice, they are no help at all.