Seeing a SIP 403 “Forbidden” Error? Here’s What To Do

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A SIP 403 “Forbidden” error means that the server understands your request, but refuses to fulfill it.

Most people encounter this error when their login credentials are wrong or missing, when the destination that they’re calling is unavailable, or when they’re registering too many devices too quickly.

Before we dive into how to fix a SIP 403, it’s good to know what’s happening to a system when the error occurs.

SIP 403: What’s Really Going On

Session initiation protocol (SIP) starts, maintains, and ends IP-based phone calls. It makes you available to another party, connects you to one, and then allows the call to continue until one party decides to end it.

SIP authenticates through a series of requests and responses between parties. Requests are codes sent to the server that establish communication, and responses are codes sent back, indicating whether or not the request was successful.

Graphic to show how SIP trunking works in a VoIP business phone system.

If you get a response with a three-digit error code that starts with the number 4, it indicates a client response failure.

The SIP 403 error code, in particular, means that the server understood the request but refused to fulfill it for some reason.

Why A SIP 403 Response Happens

Common reasons a SIP 403 error might occur are:

  • The call has been rejected by the receiver
  • A wrong username or password
  • The call destination is not allowed
  • Incorrect international dialing prefix
  • Insufficient account balance
  • Trying to register multiple devices at the same time
  • Trying to register too quickly
  • Calling a blocked number
  • Too many failed registrations
  • The SIP account was blocked or deleted by a Private Branch Exchange (PBX)
  • A general routing issue
  • Problems with the IP or call number

Because there are so many reasons a SIP 403 error might occur, it can be difficult to diagnose why it’s happening to you.

Common Fixes for SIP 403 Responses

The good news is that just about every issue that causes a SIP 403 response has some sort of practical solution.

The call has been rejected by the receiver

Often, a SIP 403 error happens because the call is rejected by the receiver. Make sure you’re calling the right person. 

It’s also ideal if you can ensure the person is expecting your call so that they don’t reject it. For example, scheduling the time and day you’ll call via an initial outreach email. 

Wrong username or password

In some instances, you may be prompted to enter an authentication username or password before sending a SIP request. Mistyping a username or password can result in a SIP 403 response. 

Take a moment to enter the correct username and password. If you lost, forgot, or never received your authentication username and login credentials, contact your VoIP provider for them. Also, contact your provider if you have your authentication credentials but they aren’t working.

The call destination is not allowed

Sometimes outbound VoIP calls to certain destinations, such as other countries, are not allowed. Check with your VoIP provider to confirm who and where you can call. You might also be able to expand your plan to support calls internationally and to other restricted areas. 

Incorrect international dialing prefix

When making calls to international destinations, you’ll be prompted to enter the country’s international call prefix before the number itself. Double-check to make sure the call prefix is correct—if not, you’ll likely receive a SIP 403 error code.

Insufficient account balance

Many VoIP phone providers require you to pay for minutes for outbound calls. If you don’t have enough money in your account when trying to make a call, it can result in a 403 error code. 

Double-check your account balance and replenish it before calling again.

Trying to register multiple devices at the same time

Registering multiple devices with a VoIP provider simultaneously can sometimes cause a SIP 403 error code.

If you want to register more than one device, be sure to register them one at a time as a way to avoid a SIP 403 error.

Trying to register too quickly

Trying to register a new device too soon after a previous registration can also return a 403 error. Give the server some time to process each registration (10-20 minutes) and only proceed once you receive a “success” notification. Then, you can move forward with registering your next device.

Calling a blocked number

Calling a blocked number will almost certainly result in a SIP 403 error. If you have another VoIP number or a traditional phone, try calling again from one of these numbers to see if you can get through. Chances are the person you’re calling won’t have all of your numbers blocked.

Too many failed registrations

Trying to register a device or multiple devices too many times unsuccessfully will likely result in a 403 error code.

Be sure to follow the registration steps carefully and have all the available information you need ahead of time. You’ll usually get an email from your provider on what you need for registration once you sign up for their service. This information might also be available on their website. 

Contact your provider if you continue to encounter a SIP 403 error from too many failed registration attempts.

SIP account may have been blocked or deleted by PBX

A blocked or deleted SIP account is another reason for 403 Forbidden errors. Check with your provider to see if your SIP account has been blocked or deleted and what the next steps are in getting your access restored.

A routing issue may have occurred

Sometimes, routing problems beyond your control can cause recurrent 403 error codes when making VoIP calls. Restart your router first to see if this resolves the issue. If not, troubleshoot your router via your provider’s app or online interface. If this doesn’t reveal the issue, contact your provider to see if they can give you insight into any issues with your router impacting your ability to make VoIP calls.

Problems with the IP or call number

In some cases, there may be problems with the IP itself or the number you’re trying to call for unknown reasons. Confirm the IP address or phone number is correct from what you know. If it is, contact your provider to see if they’re able to identify and fix the issue on their end.

What To Do If You’re Still Getting A SIP 403 Error After Trying All of These Fixes

If you’re still getting the SIP 403 error code after trying all of these fixes, additional troubleshooting with the help of your provider is probably required. They have more tools at their disposal, as well as access to additional data that could diagnose your particular issue. Call your provider if you can’t figure out a workaround for the SIP 403 error on your own.

SIP 403 vs. Other Request Failures

The SIP 403 error code is just one of several 4XX errors that can occur due to client response failures.

Having a better understanding of the different error codes in the 400’s can help you troubleshoot a range of client response failure issues with your VoIP phone and solve them without having to call your provider for everything.

  • 400 Bad Request: This indicates that the server couldn’t understand the request due to a syntax error.
  • 401 Unauthorized: Authentication is needed to complete the request.
  • 404 Not Found: The address or user requested doesn’t exist.
  • 405 Method Not Allowed: The method of the request is understood but it’s not permitted by the destination address.
  • 406 Not Acceptable: The response isn’t able to be processed due to an unfulfilled requirement in the request code.
  • 408 Request Timeout: The server wasn’t able to locate the user in a suitable amount of time.
  • 410 Gone: The user being contacted is no longer available.
  • 480 Temporarily Unavailable: the number you’re trying to call is unreachable

This list of codes may seem long, especially if you’re solely responsible for learning about each one. Fortunately, most of these SIP codes are common and have reasonable fixes that you can execute on your own, saving your provider’s time for customers who really need them. 

Mikki Akins is a writer and content creator for B2B and B2C audiences. She writes on various subjects, including business communications, marketing, and technology. She also enjoys writing poetry, short stories, and personal narratives. Aside from writing and content creation, she enjoys spending time with loved ones, immersing herself in nature, and exploring all the wonders of the world.

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