Microsoft Teams Phone: Error Code 412 Fix – Causes & Troubleshooting

Microsoft Teams Phone Error Code 412 usually appears when an inbound Direct Routing call reaches Teams with a target number that cannot be parsed into a valid callee MRI (Messaging Resource Identifier). In Microsoft’s own mapping, this pattern is tied to Microsoft response code 510412 together with SIP 412, so the fastest repair path is to inspect the called number, its format, and the translation applied before the call lands in Teams. [✅Source-1]

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What Error Code 412 Means in Teams Phone

For Direct Routing work, the plain SIP phrase by itself is not enough. Engineers often compare cases like this with other documented Microsoft Teams Direct Routing error codes to understand whether the failure belongs to number parsing, routing logic, or signaling behavior. Microsoft’s troubleshooting guidance says to read the Microsoft response code together with the SIP code because that pairing tells you far more about the actual failure path. When the pair is 510412 + 412, Microsoft labels it as wrong callee MRI, which points the investigation toward the inbound destination number rather than toward a random media problem. [✅Source-2]

Why This Error Appears

Wrong number in, failed call out. That is usually the story here. Teams expects a destination string it can route cleanly. If the inbound callee number arrives in a carrier-local pattern, keeps a trunk prefix that should have been removed, carries an unexpected URI-style prefix, or reaches Teams without the translation rule that your SBC plan assumed, the call can fail before normal routing finishes.

1. The PSTN or SBC sends the called number in a local format while Teams expects a routable canonical format.
2. An inbound number translation rule is missing, skipped, or built for the wrong pattern.
3. The number includes a domestic or international access prefix that should not survive into the Teams-facing target string.
4. An extension-based destination is written in a format that Teams does not treat as the assigned number.

Microsoft’s number-translation documentation is explicit here: translation rules can be used for inbound calls as well as outbound ones, and they exist to keep number formats synchronized between the tenant and the SBC side. If your carrier or gateway sends a destination string that does not match what Teams expects, this is often the section of the configuration that needs attention. [✅Source-4]

Format consistency matters more than many admins think. Microsoft’s number-format reference notes that the E.164 format allows a maximum of 15 digits, uses the plus sign to represent the international call prefix, and often drops domestic trunk prefixes when the call is represented in international form. Tiny differences, large effect. [✅Source-5]

A related Microsoft troubleshooting article on inbound Direct Routing calls shows how even a simple mismatch around a leading plus sign can cause inbound call handling logic to miss its match. Different symptom, same lesson: keep the number pattern consistent across every hop. [✅Source-6]

Where to Check the Failed Call

Sometimes the SIP ladder says it plainly. Do not guess. Open the failed call and read the record end to end.

1. Go to Analytics & reports in the Teams admin center.
2. Open Usage reports and run the PSTN Usage report.
3. Switch to the Direct Routing tab.
4. Select the affected call and inspect the Final SIP code, Final Microsoft subcode, and Final SIP phrase.
5. Open SIP Call Flow and inspect the message sequence around the inbound invite and the called number.

Microsoft’s SIP Call Flow view in the Teams admin center shows the chronological exchange between your SBC and Microsoft’s SIP Proxy. It is built for this exact sort of fault isolation. Microsoft also notes two timing limits that matter during investigations: call data can take up to 30 minutes to appear, and records older than 30 days are not available in SIP Call Flow. [✅Source-7]

How to Fix the Number Path

Normalize the Called Number Before It Reaches Teams

The repair usually starts on the inbound destination string. Make the target number that leaves the SBC and reaches Teams match the number that Teams is expected to route. If your carrier sends national format, convert it. If a trunk prefix survives into the Teams-facing leg, strip it. If one route uses E.164 and another uses a local pattern, pick one standard and keep it across the whole path. Translation rules exist for exactly this synchronization job. [✅Source-8]

• Match the inbound target to the assigned Teams number or resource account number.
• Prefer one stable representation of the number across the tenant, the SBC, and the carrier handoff.
• Remove access prefixes that should not be present in the Teams-facing destination.
• Keep country code handling consistent. Mixed habits here produce mixed results.

PowerShell and Assignment Checks

Once the number path looks clean, verify the receiving account. Microsoft’s Direct Routing setup steps say the user must be homed online, and if an old on-premises line setting still exists, you may need to clear it before managing the number online. Microsoft also documents the exact checks for RegistrarPool, OnPremLineUri, and LineUri. [✅Source-9]

Get-CsOnlineUser -Identity "user@contoso.com" | fl RegistrarPool,OnPremLineUri,LineUri

Set-CsPhoneNumberAssignment -Identity "user@contoso.com" -PhoneNumber "+14255551234" -PhoneNumberType DirectRouting

For extension-based assignments, Microsoft supports formats such as +1206555000;ext=1234. The same documentation also states that the assigned phone number cannot include the tel: prefix. Those two details save a lot of wasted testing. [✅Source-10]

Set-CsPhoneNumberAssignment -Identity "user@contoso.com" -PhoneNumber "+14255551000;ext=1234" -PhoneNumberType DirectRouting

Run the Built-In Direct Routing Diagnostic

Use Microsoft’s own Run Tests diagnostic before and after you edit routing or numbering rules. The Direct Routing diagnostic in the Microsoft 365 admin center checks whether the user is configured correctly and points to tenant, user, or policy gaps when it finds one. It is fast, useful, and easy to overlook. [✅Source-11]

When the Issue Points Beyond Number Parsing

If the call record shows 510412 + 412, stay on the numbering path first. Still, it is wise to glance at broader SBC health signals in parallel. Microsoft’s Direct Routing monitoring article says SIP options are normally sent every minute, and the service treats an SBC as healthy when options were seen during the last three minutes. If those health signals are missing, fix them too, even if they are not the first cause of this exact 412 mapping. [✅Source-12]

Health Dashboard adds another useful layer. Microsoft says the dashboard warns when an SBC certificate is due to expire within 30 days. It also notes that the average duration of a 1:1 PSTN call is usually around four to five minutes, while very short averages such as 15 seconds can suggest broader calling reliability trouble. The same page gives the NER formula as 100 × (Answered calls + User Busy + Ring no Answer + Terminal Reject Seizures) / Total Calls. These numbers help separate a narrow number parsing fault from a wider service health problem. [✅Source-13]

If you also see outbound routing oddities around the same number range, review the effective dial plan as well. Microsoft’s dial-plan documentation explains that Teams uses normalization rules to translate user-entered numbers into a standardized format, typically E.164, before routing. That will not be the first fix for an inbound 510412 case, but it is often relevant when numbering problems appear on both directions of the same route family. [✅Source-14]

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