ItsGamingTubeYT the status code is 500, so something was logged on the server side. I've browsed your logs, this is the error that we are interested in:
[2022-04-09 06:38:39] flarum.ERROR: exception 'Aws\S3\Exception\S3Exception' with message 'Error executing "PutObject" on "//xxx.n1.artiom.host:xxxx/2022-04-09/1649486318-839230-happy.png"; AWS HTTP error: cURL error 6: Could not resolve host: xxx.n1.artiom.host (see https://curl.haxx.se/libcurl/c/libcurl-errors.html) for http://xxx.n1.artiom.host:xxx/2022-04-09/1649486318-839230-happy.png'
GuzzleHttp\Exception\ConnectException: cURL error 6: Could not resolve host: xxx.n1.artiom.host (see https://curl.haxx.se/libcurl/c/libcurl-errors.html) for http://xxx.n1.artiom.host:xxx/2022-04-09/1649486318-839230-happy.png in /app/vendor/guzzlehttp/guzzle/src/Handler/CurlFactory.php:210
Stack trace:
#0 /app/vendor/guzzlehttp/guzzle/src/Handler/CurlFactory.php(158): GuzzleHttp\Handler\CurlFactory::createRejection()
#1 /app/vendor/guzzlehttp/guzzle/src/Handler/CurlFactory.php(110): GuzzleHttp\Handler\CurlFactory::finishError()
#2 /app/vendor/guzzlehttp/guzzle/src/Handler/CurlMultiHandler.php(244): GuzzleHttp\Handler\CurlFactory::finish()
#3 /app/vendor/guzzlehttp/guzzle/src/Handler/CurlMultiHandler.php(168): GuzzleHttp\Handler\CurlMultiHandler->processMessages()
#4 /app/vendor/guzzlehttp/guzzle/src/Handler/CurlMultiHandler.php(183): GuzzleHttp\Handler\CurlMultiHandler->tick()
#5 /app/vendor/guzzlehttp/promises/src/Promise.php(248): GuzzleHttp\Handler\CurlMultiHandler->execute()
#6 /app/vendor/guzzlehttp/promises/src/Promise.php(224): GuzzleHttp\Promise\Promise->invokeWaitFn()
#7 /app/vendor/guzzlehttp/promises/src/Promise.php(269): GuzzleHttp\Promise\Promise->waitIfPending()
#8 /app/vendor/guzzlehttp/promises/src/Promise.php(226): GuzzleHttp\Promise\Promise->invokeWaitList()
#9 /app/vendor/guzzlehttp/promises/src/Promise.php(269): GuzzleHttp\Promise\Promise->waitIfPending()
#10 /app/vendor/guzzlehttp/promises/src/Promise.php(226): GuzzleHttp\Promise\Promise->invokeWaitList()
#11 /app/vendor/guzzlehttp/promises/src/Promise.php(62): GuzzleHttp\Promise\Promise->waitIfPending()
#12 /app/vendor/aws/aws-sdk-php/src/S3/S3ClientTrait.php(34): GuzzleHttp\Promise\Promise->wait()
#13 /app/vendor/league/flysystem-aws-s3-v3/src/AwsS3Adapter.php(606): Aws\S3\S3Client->upload()
#14 /app/vendor/league/flysystem-aws-s3-v3/src/AwsS3Adapter.php(391): League\Flysystem\AwsS3v3\AwsS3Adapter->upload()
#15 /app/vendor/fof/upload/src/Adapters/Flysystem.php(66): League\Flysystem\AwsS3v3\AwsS3Adapter->writeStream()
#16 /app/vendor/fof/upload/src/Commands/UploadHandler.php(134): FoF\Upload\Adapters\Flysystem->upload()
#17 [internal function]: FoF\Upload\Commands\UploadHandler->FoF\Upload\Commands\{closure}()
#18 /app/vendor/illuminate/collections/Collection.php(695): array_map()
#19 /app/vendor/fof/upload/src/Commands/UploadHandler.php(169): Illuminate\Support\Collection->map()
#20 /app/vendor/illuminate/bus/Dispatcher.php(122): FoF\Upload\Commands\UploadHandler->handle()
[...]
Is your configuration correct? It looks like cURL is not able to resolve that URL. Or, it doesn't seem that you're using AWS S3, so it's possible that FoF Upload isn't compatible with what you're using. But I don't have much experience with buckets, so I can't know for sure