Why does a function connection error occur?

Question

Yii

in extensions.php I registered alias for GuzzleHttp. The default_user_agent function is connected, which is located in functions.php. But for some reason it's an error. Why is that? Immediately I will say the version of php 7.4

Answer 1

Error because there is no such function in GuzzleHttp.
If you have the default_user_agent() function in the same file where the error is on the screen, then you need to do this:
return $this->default_user_agent() ..........
or
return self::default_user_agent() .... ......