Error after clicking submit button in CRUD application in PHP

Question

I have made a CRUD application. Every operation works well but update operation gives error.

This is index.php index.php`

This is update.php

update.php

This is the home page: This is after clicking UPDATE button: Here is not any error, GET method works successfully: This is after clicking submit button, the recorde is not updated.

I am trying to fix this from last 2 days. Please help me.

I am trying to make a CRUD operation.