"Exception: Cannot prepare callback CIF" when assiging lambda function as a callback in PHP FFI

Question

I am currently connecting a C library in PHP using FFI.

My current code works properly and I am now trying to call a PHP lambda function from my C code and I am stuck with the following error:

PHP Fatal error: Uncaught FFI\Exception: Cannot prepare callback CIF

The goal would be to pass the following PHP function:

fn($core, $state, $message) => var_dump($message);

As a parameter of the following C method

/**
 * Set the #LinphoneCoreGlobalStateChangedCb callback.
 * @param cbs A #LinphoneCoreCbs. @notnil
 * @param cb The callback.
 */
LINPHONE_PUBLIC void linphone_core_cbs_set_global_state_changed(LinphoneCoreCbs *cbs, LinphoneCoreCbsGlobalStateChangedCb cb);

https://gitlab.linphone.org/BC/public/liblinphone/-/blob/master/include/linphone/core.h#L359

And here is the non-working code:

$ffi = FFI::cdef("
    ...
    typedef struct LinphoneCore LinphoneCore;
    typedef struct LinphoneGlobalState LinphoneGlobalState;
    typedef void (*LinphoneCoreCbsGlobalStateChangedCb)(LinphoneCore *core, LinphoneGlobalState state, const char *message);
    typedef LinphoneCoreCbsGlobalStateChangedCb LinphoneCoreGlobalStateChangedCb;
    void linphone_core_cbs_set_global_state_changed(LinphoneCoreCbs *cbs, LinphoneCoreCbsGlobalStateChangedCb cb);
    ...
    ",
"./liblinphone.so");

$cbs = $ffi->linphone_factory_create_core_cbs($ffi->linphone_factory_get());
$func = fn($core, $state, $message) => var_dump($message);
$ffi->linphone_core_cbs_set_global_state_changed($cbs, $func);

It seems that I can directly assign lambda function to PHP FFI code like that, as stated in the documentation https://www.php.net/manual/en/ffi.examples-callback.php but I'm maybe missing something.

Thanks in advance for the help.