Error: Call to undefined function Sentry\mb_strpos()

I have issue when try to add sentry to php project. I install composer and go with instructions:
I add require ‘path to autoload.php’
install composer require sentry/sdk:2.0.3
add Sentry\init([‘dsn’ => my dns]);
add error:
try {
} catch (\Throwable $exception) {
but it make my app stop working, so I add Sentry\captureException($exception); in try catch and get Error: Call to undefined function Sentry\mb_strpos().
I have installed mb_strpos.
How to fix it?