I copy & paste the universal tracking code in the settings - SEO - Header Code, it does not work; I also tried to paste it in the Footer Code column, it does not work. 

Is there any other way to solve this issue? 

Was your site hosted somewhere else previously, @Viv? 

Thanks for asking, 

Nope, I used weebly only, and it was previously visible & searchable on google. 

I do not know what happened it suddently disappeared (but I can enter the website if I typed the full website address, so it should be already online)

I verified the google search console today, but it is still not searchable. 😕 

Too bad, are there any steps I missed or did it wrong? 

@Viv, I'm seeing a Google Analytics code in the header, and plain text in the footer. I would copy and paste what you have in the header into the footer, and then use the header code box as described here:

https://www.weebly.com/seo/search-console

Thanks for reply,
I did switched the text and code, and also followed the instruction video.

It is still not visible, I think it may take time.

@Viv I am facing a similar problem as you. My weebly paid site was indexed and visible on google for just one day and for some strange reason, it is not ranking at all (invisible) for the last five days. The only thing I noticed was that my subscription lapsed five days ago as well. Can that do it? I just noticed and renewed my plan. Is yours visible now? How long did it take for you to get visible? What did you do? Can't wait to hear!

1. Go to https://www.google.com/webmasters/tools,
2. then click "add a property",
3. you will then have a pop up come up (do not have popups blocked or it will not work)
4. , then type in your ACTUAL home page URL address (not the one while you are in editor)
5. Click ADD button
6. You will be taken to a page that  has two tabs and says to cut and past a google message like: [google52248a9305f267ba.html] DONT DO IT THIS WAY
7. Click on the tab that says: Alternate Methods.
8. Then click on the circle that says:" HTML tags
9. Now copy the meta tag that is there. (its a bit lengthy)
10. Go to your weebly editor then on the HOME page go to the page, Click on the PAGES link above
11. Click on your Home page on the left side in your list, as if you are going to edit the information there
12. Now you should have a list that says "Landing page" "Visibility" and "SEO Settings"
13. Click on SEO settings
14. scroll all the way down to the bottom.....In the HEADER section (it should be blank) past in your metatag info
15. Publish. 
16. Then go back to the Google search console and click verify. 
17. You are now going to be taken to your new Google dash board in which it will tell you info about your site. 

Viola now your set!!!

YOu may have errors that pop up now if you are using WEEBLY free because they have the crawlers blocked. Its their way to get you to pay for your site

Make sure you do not have the box checked in "hide this page from search engines" that will help others find it