I first applied for Google Adsense not long after I started my website, and was almost instantly turned down. I was disappointed at the time, but sort of put it behind me and basically decided to forget about Google Adsense.
Subsequently I learnt that Google wants your website to have at least 40 blog posts, before they will consider the website. So, I just continued with the training and creating content, and putting Google Adsense on the back burner.
Recently I decided to give it a go again. By now I had 90 blog posts, so felt brave enough to apply again.
This time, much to my delight, (and some surprise) I was approved very quickly. At last, some success, I thought.
But, then I had to add HTML code to the header of my website, and I had no idea at all how to do that.
it will be gone the next time your theme needs an update for security or compatability....
add it using a plugin like ad inserter or headers and footers
or make a child theme...
sorry to be the bearer of bad news,,,,
but i would rather you keep the adsense that as with others .. .get a warning that the code cannot be found.......
plugins only slow your site down if they are badly coded....
phil