How to verify your Ubuntu download

I have found 1 main issue with this guide. Because of this I was not able to verify my ISO using this guide. I had to google for help.
This command did not work for me:
gpg --keyid-format long --keyserver hkp://keyserver.ubuntu.com --recv-keys 0x46181433FBB75451 0xD94AA3F0EFE21092
I had to put number “80” after address like this:
gpg --keyid-format long --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys 0x46181433FBB75451 0xD94AA3F0EFE21092
For Linux beginners like me it was big deal with lot of cursing till I found what’s wrong. But I understand Linux is free open source software. I just trying to help improve this guide to save other beginners.

There is also one confusing thing:
By following step " If you don’t have the keys…" I did not get this:
gpg: Signature made Thu Apr 5 22:19:36 2018 EDT using DSA key ID 46181433FBB75451 gpg: Can't check signature: No public key gpg: Signature made Thu Apr 5 22:19:36 2018 EDT using RSA key ID D94AA3F0EFE21092 gpg: Can't check signature: No public key

But instead I just got one of the two keys (second one).
I hope the guide will be repaired. My OS from which I followed the guide: “Linux Mint 19.3”