Just spent 8 hours debugging an issue that had been sitting in my issue queue for a week. WooCommerce was claiming transactions were failing, but going through in the background anyway.

Can’t share any more specifics here, but the gist of it is that the server the code was developed on was set to PHP version 7.1, while the server the dev site was on was set to version 5.6 (which I didn’t even think was still installed, never mind the default...).

So yeah, fun times over a trivial fix.