Here's a previous thread on their codes (almost all expired):
https://www.namepros.com/threads/0-00-xyz-design-wiki-ink-registration-at-porkbun.1273221/
Here's what works right now:
.xyz, code: XYZFREE22RED
https://porkbun.com/tld/xyz/?coupon=XYZFREE22RED
.dev, code: CODENEWBIE
.app, code...