Enable apcu on php 7.3 Mac OS Mojave

Question

On PHP 7.3.6

I have installed apcu by brew.

It looks installed successfully on both browser and CLI

$ php -m | grep apc
apcu

php info on browser

apcu
APCu Support    Enabled
Version 5.1.17
APCu Debugging  Disabled
MMAP Support    Enabled
MMAP File Mask  no value
Serialization Support   php
Build Date  Jul 1 2019 12:34:19

However,Both code below shows the wrror.

\apc_exists("test");

apc_exists("test");

Attempted to call function 'apc_exists' from the global namespace. (500 Internal Server Error)

Is there any other place I need to check??