I have trouble with my website, there is a problem with logging in. When I login the admin, it failed at the first time, but it lets me in the second attempt. It shows a 400 Bad Request error with the admin-ajax.php file, anyone have any ideas? I have looked into it for a few days, but I still can not fix this problem, this problem does not happen on my other websites.
The problem may be that the default data type that .ajax() sends isn’t compatible with PHP. Include the arg dataType : ‘json’, in your .ajax() args list for compatibility. Could you please have a check?
It seems taht it is an issue you would need to ask your host about.