When You move your blog address from Blogspot.com to a custom domain automatically your moving from HTTPS which is Hyper Text Transfer Secure protocol to HTTP which is not a secure protocol.
HTTPS is a measure-nary means for ensuring that secure communication is established between a user’s browser and a web server. Any site that is HTTPS encrypted shows a green address bar or padlock in the browser window to indicate that the connection to the site is very secured.
Therefore HTTPS is strongly recommended for any business who is focused on reassuring visitors to their website, securing their website, achieving a high ranking and future proofing their online operations.
More Transparency – Prospective customers can see that you are a genuine business and you own the domain name and ready to flow with you.
More Traffic: HTTPS is one of the factors Google uses in Ranking sites, so then business using HTTPS can get a better ranking than less secure competitors.
Step 1 from your blogger dashboard.
Click on Settings.
Locate the Turn on HTTPS.
Click the drop down arrow and choose yes.
Locate the HTTPS Redirect.
Click the drop down arrow and choose yes
see images below
This simple step takes you to a secure connection.
I hope this post will be helpful, However, if you face any confusion or have any personal question, feel free to discuss in comment or contact with me from Contact page. I will try my best to stay with you.