[ydant]

Your email for verifying email address fails on Fastmail's spam rules:

   X-Sieve: CMU Sieve 3.0
   X-Spam-known-sender: no ("Email failed DMARC policy for domain")
   X-Spam-sender-reputation: 500 (none)
   X-Spam-score: 5.2
   X-Spam-hits: BAYES_20 -0.001, HEADER_FROM_DIFFERENT_DOMAINS 0.249, ME_HAS_VSSU 0.001,
     ME_QUARANTINE 5, ME_SC_NH -0.001, ME_SENDERREP_NEUTRAL 0.001,
     RCVD_IN_DNSWL_NONE -0.0001, SPF_HELO_NONE 0.001, SPF_PASS -0.001,
     UNPARSEABLE_RELAY 0.001, LANGUAGES unknown, BAYES_USED user,
     SA_VERSION 3.4.6
   X-Spam-source: IP='143.55.232.5', Host='pc232-5.mailgun.net', Country='US',
     FromHeader='biz', MailFrom='org'
   X-Spam-charsets: plain='utf-8'

Clicking the link the first time gave me a default nginx:

   502 Bad Gateway
   nginx/1.22.0 (Ubuntu)

The link worked the second time.