I created an accordion in my pages to show the name of the products in alphabetical order to help users. I inserted an Ajax function to read several URLs with the following piece of code:

e.open("GET", "https://example.com/feed.php?letter=A&id=" + myId, true);

or

e.open("GET", "https://example.com/feed.php?letter=B&id=" + myId, true);

Each URL
https://example.com/feed.php?letter=B&id=1
https://example.com/feed.php?letter=B&id=2
shows 20 links to 20 different products, and works ok for the users. The ids for each URL are taken from another JavaScript code, and the URLs are correctly created for users.

However, within my Google Search Console I find several 404 errors (one per letter), warning me that Googlebot was not able to crawl
https://example.com/feed.php?letter=B&id=
(with no value for 'id')

As I said, the accordion and the Ajax work ok in the webpages. I would like to make Googlebot to crawl correctly an Ajax URL.