ارور لاراول هنگام راه اندازی

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ورژن php : 7.1.x

Fatal error: Uncaught Error: Call to undefined function SymfonyPolyfillMbstringiconv_strpos() in /home/server/public_html/myhost/vendor/symfony/polyfill-mbstring/Mbstring.php:490 Stack trace: #0 /home/server/public_html/myhost/vendor/symfony/polyfill-mbstring/bootstrap.php(34): SymfonyPolyfillMbstringMbstring::mb_strpos(NULL, '/json', 0, 'UTF-8') #1 /home/server/public_html/myhost/vendor/laravel/framework/src/Illuminate/Support/Str.php(107): mb_strpos(NULL, '/json') #2 /home/server/public_html/myhost/vendor/laravel/framework/src/Illuminate/Http/Concerns/InteractsWithContentTypes.php(34): IlluminateSupportStr::contains(NULL, Array) #3 /home/server/public_html/myhost/vendor/laravel/framework/src/Illuminate/Http/Request.php(339): IlluminateHttpRequest->isJson() #4 /home/server/public_html/myhost/vendor/laravel/framework/src/Illuminate/Http/Request.php(400): IlluminateHttpRequest->getInputSource() #5 /home/server/public_html/myhost/vendor in /home/server/public_html/myhost/vendor/symfony/polyfill-mbstring/Mbstring.php on line 490