The CORS standard is a client-side standard, implemented in the browser. So it is the browser which prevent the call from completing and generates the error message - not the server.

Mod note: This question is about why XMLHttpRequest/fetch/etc. on the browser are subject to the Same Access Policy restrictions (you get errors mentioning CORB or CORS) while Postman is not. This question is not about how to fix a "No 'Access-Control-Allow-Origin'..." error. It's about why they happen.

Postman does not implement the CORS restrictions, which is why you don't see the same error when making the same call from Postman.

Origin=null is set when you open HTML content from a local directory, and it sends a request. The same situation is when you send a request inside an , like in the below snippet (but here the Host header is not set at all) - in general, everywhere the HTML specification says opaque origin, you can translate that to Origin=null. More information about this you can find here.</p> <h2>How to install t8 led tube lightballast bypass</h2> <p>location ~ ^/index\.php(/|$) { ... add_header 'Access-Control-Allow-Origin' "$http_origin" always; add_header 'Access-Control-Allow-Credentials' 'true' always; if ($request_method = OPTIONS) { add_header 'Access-Control-Allow-Origin' "$http_origin"; # DO NOT remove THIS LINES (doubled with outside 'if' above) add_header 'Access-Control-Allow-Credentials' 'true'; add_header 'Access-Control-Max-Age' 1728000; # cache preflight value for 20 days add_header 'Access-Control-Allow-Methods' 'GET, POST, OPTIONS'; add_header 'Access-Control-Allow-Headers' 'My-First-Header,My-Second-Header,Authorization,Content-Type,Accept,Origin'; add_header 'Content-Length' 0; add_header 'Content-Type' 'text/plain charset=UTF-8'; return 204; } }</p> <p>The solution is to encode the request as base64 or update your ModSecurity settings on nginx to no longer block the request.</p> <p>Regular web pages can use the XMLHttpRequest object to send and receive data from remote servers, but they're limited by the same origin policy. Extensions aren't so limited. An extension can talk to remote servers outside of its origin, as long as it first requests cross-origin permissions.</p> <h2>How to installT5LED tube light</h2> <p>The error you get is due to the CORS standard, which sets some restrictions on how JavaScript can perform ajax requests.</p> <h2>How to install LED tube lightfixture</h2> <p></p> <p>If you do not use a simple CORS request, usually the browser automatically also sends an OPTIONS request before sending the main request - more information is here. The snippet below shows it:</p> <p>Postman as a development tool chooses not to enforce SOP while some browsers enforce, this is why you can send requests via Postman that you cannot send with XMLHttpRequest via JS using the browser.</p> <p>You might also get this error if your gateway timeout is too short and the resource you are accessing takes longer to process than the timeout. This may be the case for complex database queries etc. Thus, the above error code can be disguishing this problem. Just check if the error code is 504 instead of 404 as in Kamil's answer or something else. If it is 504, then increasing the gateway timeout might fix the problem.</p> <p>Here is an example configuration which turns on CORS on nginx (nginx.conf file) - be very careful with setting always/"$http_origin" for nginx and "*" for Apache - this will unblock CORS from any domain (in production instead of stars use your concrete page adres which consume your api)</p> <h2>How to install LED tube lighton wall</h2> <p>Your IP address is not whitelisted, so you are getting this error. Ask the backend staff to whitelist your IP address for the service you are accessing.</p> <p>This difference in domain names triggers CORS (Cross-Origin Resource Sharing) policy called SOP (Same-Origin Policy) that enforces the use of same domains (hence Origin) in Ajax, XMLHttpRequest and other HTTP requests.</p> <p>If I understood it right you are doing an XMLHttpRequest to a different domain than your page is on. So the browser is blocking it as it usually allows a request in the same origin for security reasons. You need to do something different when you want to do a cross-domain request.</p> <p>fetch('http://example.com/api', { method: 'POST', headers: { 'Content-Type': 'application/json'} }); Look in chrome-console -> network tab to 'api' request. This is the OPTIONS request (the server does not allow sending a POST request)</p> <h2>How towireLED tubelights without ballast</h2> <p>In the below investigation as API, I use http://example.com instead of http://myApiUrl/login from your question, because this first one working. I assume that your page is on http://my-site.local:8088.</p> <p>I discovered that my Heroku database table does not contains all the columns of my local table after updating Heroku database table everything worked well.</p> <p>I know that the API or remote resource must set the header, but why did it work when I made the request via the Chrome extension Postman?</p> <p>Most browsers enforce the policy of Same-Origin Policy to prevent issues related to CSRF (Cross-Site Request Forgery) attack.</p> <h2>How to install T8 tube light</h2> <p><img src="https://i.sstatic.net/XLrRg.png" alt="Image"></p> <p>For me I got this issue for different reason, the remote domain was added to origins the deployed app works perfectly except one end point I got this issue:</p> <p>This is similar to browsers' way of sending requests when the site and API has the same domain (browsers also set the header item Referer=http://my-site.local:8088, however I don't see it in Postman). When Origin header is not set, usually servers allow such requests by default.</p> <p>I am trying to do authorization using JavaScript by connecting to the RESTful API built-in Flask. However, when I make the request, I get the following error:</p> <p>For me, I just changed the browser, then it worked. I was working on localhost. My API was on localhost:7133 and my app was on localhost:5173. In Chrome and Edge, it didn't work, but when I tried it with Opera, it worked. I think when I publish the API and web app on different domains, it will be a solution.</p> <h2>T8 LED tubeWiring Diagram</h2> <p>It's very simple to solve if you are using PHP. Just add the following script in the beginning of your PHP page which handles the request:</p> <p>Note: If you are looking for downloading content from a third-party website then this will not help you. You can try the following code, but not JavaScript.</p> <h2>How to install LED tubelights on ceiling</h2> <p>Why doesn't Postman implement CORS? CORS defines the restrictions relative to the origin (URL domain) of the page which initiates the request. But in Postman the requests doesn't originate from a page with an URL so CORS does not apply.</p> <p>In my case the CORS error could be removed by disabling the same origin policy (CORS) in the Internet Explorer browser, see How to disable same origin policy Internet Explorer. After doing this, it was a pure 504 error in the log.</p> <p>Our issue was triggered my ModSecurity on nginx. The requested never got to the PHP server and returned 403 to Google Chrome; and since we had two different domains (origin and destination) Chrome understood that the lack of Access-Control-Allow-Origin was a CORS issue.</p> <p><img src="https://i.sstatic.net/8ITev.png" alt="Image"></p> <p>WARNING: Using Access-Control-Allow-Origin: * can make your API/website vulnerable to cross-site request forgery (CSRF) attacks. Make certain you understand the risks before using this code.</p> <p>This is the standard way how Postman sends requests. But a browser sends requests differently when your site and API have different domains, and then CORS occurs and the browser automatically:</p> <p>The command above will disable chrome web security. So for example if you work on a local project and encounter CORS policy issue when trying to make a request, you can skip this type of error with the above command. Basically it will open a new chrome session.</p> <p># ------------------------------------------------------------------------------ # | Cross-domain Ajax requests | # ------------------------------------------------------------------------------ # Enable cross-origin Ajax requests. # http://code.google.com/p/html5security/wiki/CrossOriginRequestSecurity # http://enable-cors.org/ # <IfModule mod_headers.c> # Header set Access-Control-Allow-Origin "*" # </IfModule> # Header set Header set Access-Control-Allow-Origin "*" # Header always set Access-Control-Allow-Credentials "true" Access-Control-Allow-Origin "http://your-page.com:80" Header always set Access-Control-Allow-Methods "POST, GET, OPTIONS, DELETE, PUT" Header always set Access-Control-Allow-Headers "My-First-Header,My-Second-Header,Authorization, content-type, csrf-token"</p>