Deprecated (16384) : Colon prefixed route placeholders like `:foo` are deprecated. Use braced placeholders like `{foo}` instead. /home/appsites/addons/setupcase.com/testflight/vendor/cakephp/cakephp/src/Routing/Route/Route.php, line: 303 You can disable all deprecation warnings by setting `Error.errorLevel` to `E_ALL & ~E_USER_DEPRECATED`. Adding `vendor/cakephp/cakephp/src/Routing/Route/Route.php` to `Error.ignoredDeprecationPaths` in your `config/app.php` config will mute deprecations from that file only. [in /home/appsites/addons/setupcase.com/testflight/vendor/cakephp/cakephp/src/Core/functions.php, line 318]
Warning (512) : Unable to emit headers. Headers sent in file=/home/appsites/addons/setupcase.com/testflight/vendor/cakephp/cakephp/src/Error/Renderer/HtmlErrorRenderer.php line=37 [in /home/appsites/addons/setupcase.com/testflight/vendor/cakephp/cakephp/src/Http/ResponseEmitter.php, line 71]
Warning (2) : Cannot modify header information - headers already sent by (output started at /home/appsites/addons/setupcase.com/testflight/vendor/cakephp/cakephp/src/Error/Renderer/HtmlErrorRenderer.php:37) [in /home/appsites/addons/setupcase.com/testflight/vendor/cakephp/cakephp/src/Http/ResponseEmitter.php, line 168]
Warning (2) : Cannot modify header information - headers already sent by (output started at /home/appsites/addons/setupcase.com/testflight/vendor/cakephp/cakephp/src/Error/Renderer/HtmlErrorRenderer.php:37) [in /home/appsites/addons/setupcase.com/testflight/vendor/cakephp/cakephp/src/Http/ResponseEmitter.php, line 197]
Error: Could not start the session, headers already sent in file `CORE/src/Error/Renderer/HtmlErrorRenderer.php` on line `37`

Could not start the session, headers already sent in file CORE/src/Error/Renderer/HtmlErrorRenderer.php on line 37 📋

Cake\Core\Exception\CakeException
CORE/src/Http/Session.php at line 518 (edit)
                    $this->headerSentInfo['line']
                );
            }
            throw new CakeException($message);
        }
        if (!is_array($name)) {
            $name = [$name => $value];

If you want to customize this error message, create templates/Error/error500.php