Metabase 0.38 removed sql.qp/unix-timestamp->timestamp (after being deprecated since 0.35.0)
Use sql.qp/unix-timestamp->honeysql instead.
If you’re developing a custom Metabase driver and want to make sure it’s compatible with 0.38, then have look at the wiki page: https://github.com/metabase/metabase/wiki/What’s-new-in-0.38.0-for-Metabase-driver-authors