They are called 400 errors because there are different types such as 401, 402, 403, 404.
Normally, you will get a 404 error, which means the URL does not exist.
400 - This is due to a "bad request" or "null request" or a permissions problem in our .htaccess.
401 - This is an authorization failure, usually when entering username and password.
403 - This is a failure to access a file for which you do not have permission.
404 - The most classic of all, it occurs when we access a URL that does not exist.
406 - Occurs when we request something that cannot be interpreted by the server.
It is very normal for URLs to appear and disappear on a domain over time.
Google believes that having 400 errors gives a bad experience to users, and although this is something that happens in almost all domains, we have to solve it.
To fix this, you just need to access the code of the URL where you are getting the error and delete the broken link (sometimes it can also be due to a blockage of the site you are linking to).
There are SEOs who use systems to prevent these types of errors from ever appearing, but in my opinion this is totally inadvisable. If there is an error (whatever it may be) it is better to know that it exists and fix it.
A good practice is to create a good error page so that the user is located when they encounter a 404 and have a good user experience.
Take advantage of these types of pages to direct users where they really need to go.
Sitemap.xml file has format errors
Sitemaps are files that we use to tell Google where our domain information is number code philippines located. In fact, when it accesses our domain to see if we have something new or modified, it always goes to these files to find out.
It is very common in some CMS such as Joomla, PrestaShop and custom developments, that the sitemap.xml is not generated correctly or that it is even blocking access to Google through the robots.txt file (we will explain what this file is later).
If we have a problem in the sitemap.xml we will mislead Google about what it has to index, we must always ensure that this file is correct.
To solve this, I always advise you to go to a programmer.
It is something so important that it will always be worth solving no matter what the cost.
Another tip when using a sitemap is to segment the information, that is, offer different sitemaps for Google to access independently.
In Google Help you can find an explanation for creating different types of specific sitemaps: videos, images, pages, articles…
Another advantage of segmenting information is that if you have a fault in one of these files, it will always be easier for you to detect where it is located.
In Search Console you have the option to add the sitemaps you have created and, in this way, you will also see if they are correct.
If you have created or modified any sitemap.xml on your domain, I recommend that you delete it from Search Console and re-upload it, this is a way to ensure that they are crawled.