How to fix "This email address isn't in an allowed domain. To make changes to the allowed domain list, update your security settings." in your Google Ads account.
This error happens when the domain of the email address you're trying to add is not in your allowed domains list.
You just need to follow these few simple steps:
Copy the domain of the email you want to add to your Google Ads account. For example: firstname.lastname@example.org; the domain here is clickguard.com
Go to your ADMIN settings, then click on Access and Security → Security → Allowed domains
Once you click on Allowed domains, just paste the domain of the email you want to add.
Then click SAVE.
Try granting access again.