How to properly mark up a page with microdata?

Question

HTML

Hello. Such a situation: I mark up a simple page with micro-markup (I’m not particularly familiar with it, I read it a day or two). The site has contacts, and a table with services and products.
Everything is ok with the goods, I marked it through google, checked it in Yandex, there are no errors, JSON-LD markup.
The next step is to label the items. There are fields: the product itself, an example, (I think it will be clearer) iphone x silver, 1 piece, price 5000 rubles, amount 5000 rubles.
Marked up, got a bunch of errors, corrected, got more others.
It turns out if I take the markup of a separate product (html itself) and check - all the rules, but if you check this code as part of the entire site - errors appear.
I realized that here you only need to mark the name and price.
I know this is fixed, I already solved it, but sometimes it takes a lot of time, which, unfortunately, is not there now.
From the information I read, I realized that this is done only with microdata, JSON-LD is not suitable here (most likely I'm wrong)
If I mark up this data using JSON-LD, there are no errors, everything is correct.
But here I have a question: after all, the JSON-LD markup must be in front of how the search engine will understand that everything is correct and give the correct answer to the request. I probably didn't read it...
And in the header there will be such a code for each product,
Or should it be output to another file, or just compress (minimize) and leave it in the header, please enlighten!

Answer 1

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Answer 2

Google Markup Tool https://www.google.ru/webmasters/markup-helper/?pli=1
Checking Google markup https://developers.google.com/structured-data/test...