Load tcpdf

hi, sorry for english ,  in my localhost i install tcpdf with composer , in controller i use :
use TCPDF;
and everything work
Online server:
-i insert the tecnickcom  folder in vendor folder 
-update composer.json
 but i have this error :  class TCPDF not found 
Wat's wrong ?

maybe try :

Code:

composer dump-autoload

did it work " another approach is to define in autoload.php thats what i did with PHPMailer ; which has a names ; if no namespace you can use Classmap section of Autoload.php located : yourApp/app/Config/Autoload.php

maybe try :

Code:

composer dump-autoload

How can do this command  online ?

---

try to update on local and copy the folder composer online but i have :

Composer detected issues in your platform: Your Composer dependencies require a PHP version ">= 7.4.0".

Wats the correct way to update library ?