Can't write image data to path (Laravel)

I'm not able to save anything to the storage directory in a Laravel project and receive the following error:

I've spent the last three weeks trying to find out why I can't save images to the Storage folder in Laravel with no luck. I've scoured StackOverflow and have come to the conclusion that it's probably due to my Docker image. I'd love to use my custom images if possible but get them working. Here's my setup:

Dockerfile (base image)

ARG VERSION=7.4
FROM php:${VERSION}-fpm-alpine

# PHP_CPPFLAGS are used by the docker-php-ext-* scripts
ENV PHP_CPPFLAGS="$PHP_CPPFLAGS"

# Install zip for csv stuff
# hadolint ignore=DL3018
RUN apk add --no-cache \
    libzip-dev \
    zip \
&& docker-php-ext-install zip \
&& apk del libzip-dev

# Install gd for image stuff
# hadolint ignore=DL3018
RUN apk add --no-cache libpng libpng-dev libjpeg-turbo-dev libwebp-dev zlib-dev libxpm-dev \
    && docker-php-ext-install gd \
    && apk del libpng-dev libjpeg-turbo-dev libwebp-dev zlib-dev libxpm-dev

# Install Nginx & PHP packages and extensions
# hadolint ignore=DL3018
RUN apk add --no-cache \
    # for PHP/Laravel
    git \
    icu-dev \
    msmtp \
    nginx \
    unzip \
    # zip \
    && mkdir -p /run/nginx \
    && docker-php-ext-install \
        pdo_mysql \
        opcache \
    && { \
        echo 'opcache.memory_consumption=128'; \
        echo 'opcache.interned_strings_buffer=8'; \
        echo 'opcache.max_accelerated_files=4000'; \
        echo 'opcache.revalidate_freq=2'; \
        echo 'opcache.fast_shutdown=1'; \
        echo 'opcache.enable_cli=1'; \
    } > /usr/local/etc/php/conf.d/php-opocache-cfg.ini \
    && apk del icu-dev

COPY /config/nginx.conf /etc/nginx/conf.d/default.conf
COPY /config/msmtprc /etc/msmtprc
COPY /scripts/start.sh /etc/start.sh
COPY --chown=www-data:www-data src/ /var/www/html

WORKDIR /var/www/html

EXPOSE 80 443

ENTRYPOINT ["/etc/start.sh"]

Dockerfile (project, references the Dockerfile above ^)

FROM justintime50/nginx-php:dev # the dockerfile above

COPY --chown=www-data:www-data ./src /var/www/html
COPY nginx.conf /etc/nginx/conf.d/default.conf
RUN php composer.phar install -q --no-ansi --no-interaction --no-scripts --no-suggest --no-progress --prefer-dist \
    && chmod -R 775 storage \
    && php artisan storage:link \
    && chmod -R 775 bootstrap/cache

Docker Compose

version: "3.7"
services:

    laraview:
        build: .
        restart: always
        container_name: laraview
        volumes: 
            - ./src/storage:/var/www/html/storage
        networks:
            - traefik
            - laraview
        labels:
            - traefik.enable=true
            - traefik.docker.network=traefik
            - traefik.frontend.rule=Host:laraview.localhost
            - traefik.port=80
        env_file:
            - init-db.env
        depends_on:
            - laraview-db

    laraview-db:
        image: mysql:8.0.18
        restart: always
        container_name: laraview-db
        env_file:
            - init-db.env
        volumes:
            - ./db:/var/lib/mysql
        networks:
            - laraview
        ports:
            - "3306:3306"
        labels:
            - traefik.enable=false

networks:
    traefik:
        external:
            name: traefik
    laraview:
        name: laraview

Upload Image File (Laravel)

    public function updateProfilePic(Request $request)
    {
        $request->validate([
            'upload_profile_pic' => 'required|image|mimes:jpeg,jpg,png|max:2048',
        ]);
        $id = request()->get('id');

        $file = $request->file('upload_profile_pic');
        $img = Image::make($file)
            ->resize(320, 240)
            ->save(storage_path(), $file->getClientOriginalName());

        // Upload Profil Pic (IMAGE INTERVENTION - LARAVEL)
        //Image::make($request->file('upload_profile_pic'))->fit(150, 150)->save(storage_path('avatars/'.$id.'.png'));

        session()->flash("message", "Profile picture updated successfully.");
        return redirect()->back();
    }

References:

• Nginx/PHP image: https://github.com/Justintime50/nginx-php-docker/tree/develop
• Laravel project: https://github.com/Justintime50/laraview/tree/develop

@leo I apologize I never came back to answer this. I don't remember the exact fix but I believe I was misusing storage_path. Here is the corrected PHP code:

    public function uploadPostImage(Request $request)
    {
        $request->validate([
            'upload_image' => 'required|image|mimes:jpeg,jpg,png|max:2048',
        ]);
        $id = mt_rand(100000000000, 999999999999); # TODO: This is hacky, fix down the road

        if (!is_dir(storage_path("app/public/post-images"))) {
            mkdir(storage_path("app/public/post-images"), 0775, true);
        }

        // Upload Avatar (IMAGE INTERVENTION - LARAVEL)
        Image::make($request->file("upload_image"))->save(storage_path("app/public/post-images/".$id.".png"));

        session()->flash("message", "Image uploaded successfully.");
        return redirect()->back();
    }

I used the same Docker image and docker-compose file which means it must have been fixed by using storage_path correctly.