callback: in Select Advanced not working?

Hi there,
I'm working on a new site that allows you to track game progress.

The site is set up like so:
I have 2 custom post types: Games (slug: game) and Collectibles (slug: collectible)

Game has the following custom fields (Field group ID: cf_game)
Group: Collectible types (ID: gameCollectibleTypes (clonable, which makes this a repeater field))
* Text: Collectible type (ID: gameCollectibleTypes_Name)

Collectible has the following custom fields (Field group ID: collectible_cf)
Text: Collectible name (ID: collectibleName (also use as post title before saving, using the rwmb_before_save_post action))
Select advanced: Collectible type (ID: collectibleType)

I want to use the values in the gameCollectibleTypes repeater in the collectibleType field.

There's a relationship between the game and the collectible named: Game - Collectible (ID: game-collectible)
This contains the game the collectible is linked to.

Claude wrote me the following code to use for the callback function so that the values fill dynamically:

add_filter('collectibleType_options', 'populate_collectibleType_options');

function populate_collectibleType_options($collectibleOptions) {
    // Check if we're editing a collectible
    if (!isset($_GET['post'])) {
        return $collectibleOptions;
    }

    $collectibleId = intval($_GET['post']);
    
    // Get the related game using the relationship field
    $gameIds = rwmb_get_value('game-collectible', '', $collectibleId);
    
    if (empty($gameIds)) {
        return $collectibleOptions;
    }
    
    // Use the first related game (assuming a collectible is related to only one game)
    $gameId = is_array($gameIds) ? $gameIds[0] : $gameIds;
    
    // Get collectible types from the game
    $collectibleTypes = rwmb_the_value('gameCollectibleTypes', '', $gameId); // I've also tried rwmb_get_value.
    
    if (empty($collectibleTypes)) {
        return $collectibleOptions;
    }
    
    // Build options array from the collectible types
    $dynamicCollectibleOptions = [];
    foreach ($collectibleTypes as $collectibleType) {
        $collectibleName = isset($collectibleType['gameCollectibleTypes_Name']) ? $collectibleType['gameCollectibleTypes_Name'] : '';
        if (!empty($collectibleName)) {
            $dynamicCollectibleOptions[$collectibleName] = $collectibleName;
        }
    }
    
    return $dynamicCollectibleOptions;
}