Laravel .env variable always returns null

First, there is no STRIPE_SECRET inside your .env file(As per before edit the question). So please make sure that your .env must have this variable. You should clear your configuration cache by executing following commands in the same order

php artisan config:cache
php artisan config:clear 

Laravel cache your configuration files so the execution become faster. So everytime when you change the configuration files on server, you should clear the cache.

Additionally you can run these commands also to clear the other caches

php artisan cache:clear   //for clearing the cache
php artisan view:clear    //for clearing the compiled views
php artisan route:clear   //for clearing the routes cache

You can also create the routes for these commands and call the commands from the code also as

Route::get('/cache-clear', function() {
    $exitCode = Artisan::call('cache:clear');
    echo "Cache Cleard: ".$exitCode;
});

Route::get('/view-clear', function() {
    $exitCode = Artisan::call('view:clear');
    echo "View Cleard: ".$exitCode;
});

Route::get('/route-cache', function() {
    $exitCode = Artisan::call('route:cache');
    echo "Route Cached: ".$exitCode;
});

Route::get('/route-clear', function() {
    $exitCode = Artisan::call('route:clear');
    echo "Route Cache Cleared: ".$exitCode;
});

Route::get('/config-cache', function() {
    $exitCode = Artisan::call('config:cache');
    echo "Config Cached: ".$exitCode;
});

Route::get('/config-clear', function() {
    $exitCode = Artisan::call('config:clear');
    echo "Config Cache Cleared: ".$exitCode;
});

You can clear configuration cache using following commands

php artisan config:clear 
php artisan optimize
php artisan config:cache

Also make sure

If you are using the config:cache command during deployment, you must make sure that you are only calling the env function from within your configuration files, and not from anywhere else in your application. If you are calling env from within your application, it is strongly recommended you add proper configuration values to your configuration files and call env from that location instead, allowing you to convert your env calls to config calls.

Reference link:

Update 1:

Also make sure you have renamed .env.example to .env file by default laravel have .env.example

Update 2

As per your new update question your env file have STRIPE not STRIPE_SECRET so you have access like this if its not typo error in question

env('STRIPE')

if you have STRIPE="a12345" this in .env file or if you any change in .env file or config file then you fallow these steps

one more thing write the variable value in comma's like STRIPE="a12345"

First run these commands

 1. php artisan config:clear
 2. php artisan cache:clear
 3. composer dump-autoload

and finally used this command to get variable

dd(env('STRIPE'));

this working for me

and also 1 stupid suggestion: restart server

I have add all possible solution

The main reason upon your issue is that you are caching your configuration. When running php artisan config:cache you're storing your configuration in your cache, and the next time Laravel will boot up it won't read the .env file because it detects that the configuration has been stored in the cache. Environment file should be used only to setup configuration files and then to access the value you're looking for you should use ONLY the config method.

Let's assume that you have the file config/stripe.php that consists of this content:

<?php

return [
    'secret' => env('STRIPE_SECRET', '')
];

Once you run php artisan config:cache access this value using ONLY the syntax config('stripe.secret') through your application code. Every time you update your config files and your .env you need to run php artisan config:cache again.