If you had signup for Adsense account when you had your site or blog on blogger.com domain, then if you place the code on site after shifting from (blogger.com) to your custom domain then Adsense won’t work.
Because when you signup for AdSense account through (blogger.com) a host partner website then you get Adsense account that is limited to show ads on host partner site.
Host partner website
Host partners allow you to monetize the content you create on their websites by linking it to your AdSense account. If you’re associated with an AdSense host partner, you’ll see their name listed on the Account settings page in your account, in the “Access and authorization” section, under “3rd-party access.”
Adsense account that is created through host partner site has a red label on top of AdSense account.So you won’t be able to run an ad on the custom domain or self-controlled website.
To run ad through your AdSense account on yourself controlled site you need simple setting
Log into your Adsense account then Go to Account setting>Sites authorized to show ads filed>then press>edit.
Then a new page will open, enter the name of your website in the text in front of I will show the ad on.Then click on submit button.
Then implement an ad code on your website and wait for 2-3 days and let AdSense team review your site. After the review is completed, your website will start showing ad.