How to add DKIM signature to my emails ?

How to add DKIM signature to my emails ?

I created the dns entries of my domain following instructions from the link


Below however I can not use DKIM in my field when sending emails to gmail me I have this message

Gmail could not verifify that gustavofsantos.com.br sent this message (and not a spammer)

What i need do?

I try step by step guide

https://www.zoho.com/mail/help/adminconsole/dkim-configuration.html

 but that does not list my domains how you can see in this image