Answers.Body: <p>You're getting that error because CSRF validation is failing.  Whether that's a bug in the Dev Preview of Craft 3 or something environmental on your end is hard to tell with the given information.  I can't reproduce it locally, though.</p>
  
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2016-06-28T23:26:03.157Z
Answers.LastActivityDate: 2016-06-28T23:26:03.157Z
Answers.UserDisplayName: Brad Bell
Body: <p>When I try to install <a href="https://craftcms.com/3" rel="nofollow">Craft CMS 3</a> by going to <code>/admin</code> the site redirects me to <code>/index.php?p=admin/install</code> where the Begin button shows. Clicking next send me to the screen to create an admin user. </p>
  
  <p>When I enter all the information I see an ajax call going to <code>http://domain.com/index.php?p=admin/actions/install/validate-account</code> but that responds with 400 Error. </p>
  
  <p>Any idea whats wrong? I have .htaccess file in place, so not sure why I see the index.php part in the url. Any help would be appreciated.
  Edit: in the error log file I see those three lines</p>
  
  <pre><code>[-][-][error][yii\i18n\PhpMessageSource::loadMessages] The message file for category 'yii' does not exist: /home/rrznjzkn/public_html/craft3/craft/app/vendor/yiisoft/yii2/messages/en-US/yii.php Fallback file does not exist as well: /home/rrznjzkn/public_html/craft3/craft/app/vendor/yiisoft/yii2/messages/en/yii.php
  
  [-][-][warning][craft\app\web\ErrorHandler::handleException] 400 - Unable to verify your data submission.
  
  [-][-][error][yii\web\HttpException:400] exception 'yii\web\BadRequestHttpException' with message 'Unable to verify your data submission.' in /home/rrznjzkn/public_html/craft3/craft/app/vendor/yiisoft/yii2/web/Controller.php:110
  </code></pre>
  
Comments.ContentLicense: CC BY-SA 3.0
Comments.CreationDate: 2016-06-28T16:30:30.403Z
Comments.Text: I wouldn't recommend using Craft 3 yet... it's still in "developer preview", it hasn't even reached the "beta" phase yet. You might want to stick with the current version of Craft 2 until some formal announcements are made about 3.
Comments.UserDisplayName: Lindsey D
Comments.ContentLicense: CC BY-SA 3.0
Comments.CreationDate: 2016-06-28T20:50:03.690Z
Comments.Text: @Lindsey D: I tend to agree with you on [this](http://meta.craftcms.stackexchange.com/a/126/1016) and would vote to close it but I don't think it's an "official" stance of the community yet...
Comments.UserDisplayName: RitterKnight
Comments.ContentLicense: CC BY-SA 3.0
Comments.CreationDate: 2016-06-28T20:55:12.930Z
Comments.Text: @RitterKnight: Yeah, that's fair. I didn't VTC... just giving the OP a warning about being in uncharted territory. :)
Comments.UserDisplayName: Lindsey D
Comments.ContentLicense: CC BY-SA 3.0
Comments.CreationDate: 2016-06-29T10:19:31.147Z
Comments.Text: OK, thank you. I will stick with Craft 2 for now.
Comments.UserDisplayName: svetlin
Comments.ContentLicense: CC BY-SA 3.0
Comments.CreationDate: 2017-11-28T13:47:06.050Z
Comments.Text: Same problem with craft 2.6
Comments.UserDisplayName: dazz
Tags: <error><install><404><craft3>
Title: 400 error on Craft 3 installation
ThreadText: # 400 error on Craft 3 installation
  
  (Asked by: username_0 on 2016-06-28)
  
  When I try to install [Craft CMS 3](https://craftcms.com/3) by going to `/admin` the site redirects me to `/index.php?p=admin/install` where the Begin button shows. Clicking next send me to the screen to create an admin user.
  
  When I enter all the information I see an ajax call going to `http://domain.com/index.php?p=admin/actions/install/validate-account` but that responds with 400 Error.
  
  Any idea whats wrong? I have .htaccess file in place, so not sure why I see the index.php part in the url. Any help would be appreciated.
  Edit: in the error log file I see those three lines
  
  ```
  [-][-][error][yii\i18n\PhpMessageSource::loadMessages] The message file for category 'yii' does not exist: /home/rrznjzkn/public_html/craft3/craft/app/vendor/yiisoft/yii2/messages/en-US/yii.php Fallback file does not exist as well: /home/rrznjzkn/public_html/craft3/craft/app/vendor/yiisoft/yii2/messages/en/yii.php
  
  [-][-][warning][craft\app\web\ErrorHandler::handleException] 400 - Unable to verify your data submission.
  
  [-][-][error][yii\web\HttpException:400] exception 'yii\web\BadRequestHttpException' with message 'Unable to verify your data submission.' in /home/rrznjzkn/public_html/craft3/craft/app/vendor/yiisoft/yii2/web/Controller.php:110
  
  ```
  
  **Tags:** error, install, 404, craft3
  
  > **Comments:**
  > **username_1**: I wouldn't recommend using Craft 3 yet... it's still in "developer preview", it hasn't even reached the "beta" phase yet. You might want to stick with the current version of Craft 2 until some formal announcements are made about 3.  
  > **username_2**: @username_1: I tend to agree with you on [this](http://meta.craftcms.stackexchange.com/a/126/1016) and would vote to close it but I don't think it's an "official" stance of the community yet...  
  > **username_1**: @username_2: Yeah, that's fair. I didn't VTC... just giving the OP a warning about being in uncharted territory. :)  
  > **username_0**: OK, thank you. I will stick with Craft 2 for now.  
  > **username_3**: Same problem with craft 2.6  
  
  ---
  
  ## 1 answers
  
  ### Answer by username_4 on 2016-06-28. Score: 1
  
  You're getting that error because CSRF validation is failing. Whether that's a bug in the Dev Preview of Craft 3 or something environmental on your end is hard to tell with the given information. I can't reproduce it locally, though.
  
  
  ---
  
  