a few words about web development

Limit of 1000 fields in POST method

One setting away from fixing the problem
If you have a HTML form with over 1000 fields (for example checkboxes) and after submitting the form to your PHP script you see only the first 1000 fields you should change php.ini directive max_input_vars to a bigger value, for example:
max_input_vars = 5000
You need to change this value in your php.ini. It may be either php.ini of your Apache, eg.:
Or php.ini placed inside root directory of a website, eg.:
or .user.ini:
Or even inside .htaccess file.