Working Postfix and Gmail relay, but isnt using my own domain mail

Hi, I configured Postfix and Gmail as relayhost on my Linode following this guide https://www.linode.com/docs/guides/configure-postfix-to-send-mail-using-gmail-and-google-workspace-on-debian-or-ubuntu/. It is working but when I send a mail from my own domain, the sender is my gmail address. I would like this to be my own domain address (contact@example.com). I followed this extra tutorial https://jichu4n.com/posts/custom-domain-e-mails-with-postfix-and-gmail-the-missing-tutorial/. It seems perfect for my problem, however I can't connect to my server in step 4 via all the possible options TLS/SSL, different ports.
These are my error messages in mail.log.
Aug 5 11:23:17 mail postfix/smtpd[44161]: connect from mail-yb1-xb2e.google.com[2607:f8b0:4864:20::b2e] Aug 5 11:23:17 mail postfix/smtpd[44161]: lost connection after CONNECT from mail-yb1-xb2e.google.com[2607:f8b0:4864:20::b2e] Aug 5 11:23:17 mail postfix/smtpd[44161]: disconnect from mail-yb1-xb2e.google.com[2607:f8b0:4864:20::b2e] commands=0/0 Aug 5 11:23:17 mail postfix/smtpd[44161]: connect from mail-yb1-f175.google.com[209.85.219.175] Aug 5 11:23:17 mail postfix/smtpd[44161]: lost connection after CONNECT from mail-yb1-f175.google.com[209.85.219.175] Aug 5 11:23:17 mail postfix/smtpd[44161]: disconnect from mail-yb1-f175.google.com[209.85.219.175] commands=0/0 Aug 5 11:26:37 mail postfix/anvil[44163]: statistics: max connection rate 1/60s for (smtp:2607:f8b0:4864:20::b2c) at Aug 5 11:22:27 Aug 5 11:26:37 mail postfix/anvil[44163]: statistics: max connection count 1 for (smtp:2607:f8b0:4864:20::b2c) at Aug 5 11:22:27 Aug 5 11:26:37 mail postfix/anvil[44163]: statistics: max cache size 4 at Aug 5 11:23:17