SIP Error 403, 603, or 608? Here's what they mean.

Carrier responses like 403 Forbidden, 603 Decline, and 608 Rejected often signal call blocking or reputation issues. But the real cause varies—and so does the fix. Start by understanding what your traffic is actually telling you.
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SIP 200
SIP 403 error
SIP 603 error
SIP 608 error

SIP errors and blocked calls cost time & money. Let's get to the bottom of this.

Understanding 403, 603, and 608 SIP codes

SIP response codes are status messages phone networks use to communicate the progress of a call attempt. Three codes in particular, 403, 603, and 608, appear when a call isn't allowed to continue. While each SIP error represents a different type of refusal, they share a common thread: the network, an intermediary, or the called party has taken action to prevent the call from completing.

SIP 403
‍(Forbidden)

What does a SIP 403 error mean?

A 403 SIP response means the network itself is blocking the call. The request is understood, but a policy, permission rule, or carrier restriction disallows it. This block usually happens at the terminating carrier or an upstream network that refuses to let the call proceed.

In simple terms:
‍It’s like going up to a door and the guard says: “You’re not allowed in here.”
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SIP 603
(Decline)

What does a SIP 603 error mean?

A 603 SIP error response means the called party or their device declined the call. The call reached their carrier, but they or their settings rejected it. This can include manual declines or automated preferences (Do Not Disturb, call screening etc.).

In simple terms:
‍It’s like calling someone and they say: “No thanks, I don't want to answer.”
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SIP 608
(Rejected)

What does a SIP 608 error mean?

A 608 means the call was blocked by an intermediary analytics system—often a spam filter, fraud engine, or carrier screening service. The call is rejected before it reaches the subscriber, and the user typically never knows it happened.

In simple terms:
A security guard stops you in the hallway before you even reach the door, because you “look suspicious.”
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The challenge behind diagnosing "blocked" call errors like 403, 603, and 608

SIP error codes don’t tell the whole story—and carriers don’t always send the right one. Understanding what really caused the block requires looking at your entire call path: your dialing system, the originating and intermediary carriers, the terminating carrier’s policies, and the attestation your calls are traveling with. Fixing the issue means solving for all of it. That’s where our team comes in.
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The team behind the shield

Meet the ARMOR® team—telecom veterans who helped shape the spam-flag ecosystem at companies like Hiya, First Orion, AT&T, Lookout, and PhoneBurner. Drawing on decades of experience launching industry-first caller ID protection solutions, we bring deep carrier relationships and real-world expertise to debugging SIP issues and safeguarding your outbound calls.
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Chris Sorensen

Chris Sorensen

CEO, Founder
Telecom Experience:
PhoneBurner, Hiya
Rick Moulton headshot

Rick Moulton

VP
Telecom Experience:
PhoneBurner, Hiya, AT&T
Kevin Reeves

Kevin Reeves

CTO
Telecom Experience:
PhoneBurner
Nick Andrews

Nick Andrews

VP of Revenue
Telecom Experience:
First Orion, Windstream
Erik Meyer headshot

Erik Meyer

Service Delivery
Telecom Experience:
AT&T, T-Mobile, Hiya

Let's turn your SIP errors into 200 OKs

Every 403, 603, and 608 erros is a live connection opportunity your team never gets. When these errors stack up, your team works harder to reach fewer customers—and your caller ID reputation suffers. Schedule a review with our team and get a clear plan to fix what’s blocking your calls.
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