When uploading and saving the favicon nothing happens

When uploading and saving the favicon for going to the next step. The following errors are showing in the console:

[Failed to load resource: the server responded with a status of 500 ()](/nl/ajax/realfavicon/generate?_wrapper_format=drupal_modal&ajax_form=1&_wrapper_format=drupal_ajax:1 Failed to load resource: the server responded with a status of 500 ())

Uncaught Drupal.AjaxError message: "\nEr is een AJAX HTTP fout opgetreden.\nHTTP Result Code: 500\nDebugging information follows.\nPath: /nl/ajax/realfavicon/generate?_wrapper_format=drupal_modal&ajax_form=1\nStatustekst: error\nAntwoordtekst: Er ging onverwacht iets fout. Probeer het later opnieuw.GuzzleHttp\\Exception\\ServerException: Server error: POST https://realfavicongenerator.net/api/favicon_generator resulted in a 500 Internal Server Error response in GuzzleHttp\\Exception\\RequestException::create() (line 111 of /var/www/html/vendor/guzzlehttp/guzzle/src/Exception/RequestException.php). GuzzleHttp\\Middleware::GuzzleHttp\\{closure}() (Line: 209)\nGuzzleHttp\\Promise\\Promise::callHandler() (Line: 158)\nGuzzleHttp\\Promise\\Promise::GuzzleHttp\\Promise\\{closure}() (Line: 52)\nGuzzleHttp\\Promise\\TaskQueue->run() (Line: 251)\nGuzzleHttp\\Promise\\Promise->invokeWaitFn() (Line: 227)\nGuzzleHttp\\Promise\\Promise->waitIfPending() (Line: 272)\nGuzzleHttp\\Promise\\Promise->invokeWaitList() (Line: 229)\nGuzzleHttp\\Promise\\Promise->waitIfPending() (Line: 69)\nGuzzleHttp\\Promise\\Promise->wait() (Line: 189)\nGuzzleHttp\\Client->request() (Line: 95)\nGuzzleHttp\\Client->post() (Line: 149)\nDrupal\\cortex_favicon\\Form\\RealFaviconGeneratorForm->submitForm()\ncall_user_func_array() (Line: 105)\nDrupal\\Core\\Form\\FormSubmitter->executeSubmitHandlers() (Line: 43)\nDrupal\\Core\\Form\\FormSubmitter->doSubmitForm() (Line: 589)\nDrupal\\Core\\Form\\FormBuilder->processForm() (Line: 144)\nDrupal\\autosave_form\\Form\\AutosaveFormBuilder->processForm() (Line: 321)\nDrupal\\Core\\Form\\FormBuilder->buildForm() (Line: 97)\nDrupal\\autosave_form\\Form\\AutosaveFormBuilder->buildForm() (Line: 73)\nDrupal\\Core\\Controller\\FormController->getContentResult()\ncall_user_func_array() (Line: 123)\nDrupal\\Core\\EventSubscriber\\EarlyRenderingControllerWrapperSubscriber->Drupal\\Core\\EventSubscriber\\{closure}() (Line: 622)\nDrupal\\Core\\Render\\Renderer->executeInRenderContext() (Line: 121)\nDrupal\\Core\\EventSubscriber\\EarlyRenderingControllerWrapperSubscriber->wrapControllerExecutionInRenderContext() (Line: 97)\nDrupal\\Core\\EventSubscriber\\EarlyRenderingControllerWrapperSubscriber->Drupal\\Core\\EventSubscriber\\{closure}() (Line: 183)\nSymfony\\Component\\HttpKernel\\HttpKernel->handleRaw() (Line: 76)\nSymfony\\Component\\HttpKernel\\HttpKernel->handle() (Line: 53)\nDrupal\\Core\\StackMiddleware\\Session->handle() (Line: 48)\nDrupal\\Core\\StackMiddleware\\KernelPreHandle->handle() (Line: 28)\nDrupal\\Core\\StackMiddleware\\ContentLength->handle() (Line: 32)\nDrupal\\big_pipe\\StackMiddleware\\ContentLength->handle() (Line: 116)\nDrupal\\page_cache\\StackMiddleware\\PageCache->pass() (Line: 90)\nDrupal\\page_cache\\StackMiddleware\\PageCache->handle() (Line: 48)\nDrupal\\Core\\StackMiddleware\\ReverseProxyMiddleware->handle() (Line: 51)\nDrupal\\Core\\StackMiddleware\\NegotiationMiddleware->handle() (Line: 53)\nDrupal\\Core\\StackMiddleware\\AjaxPageState->handle() (Line: 51)\nDrupal\\Core\\StackMiddleware\\StackedHttpKernel->handle() (Line: 715)\nDrupal\\Core\\DrupalKernel->handle() (Line: 19)\n" name:"AjaxError"stack:"Error\n at https://fons.ddev.site/core/misc/ajax.js?v=11.2.2:198:32\n at https://fons.ddev.site/core/misc/ajax.js?v=11.2.2:1928:3"[[Prototype]]: Error at https://fons.ddev.site/core/misc/ajax.js?v=11.2.2:198:32 at https://fons.ddev.site/core/misc/ajax.js?v=11.2.2:1928:3