Microsoft Teams Phone: Error Code 415 Fix – Causes & Solutions

Error Code 415 in Microsoft Teams Phone usually points to a Direct Routing signaling fault, not a generic desktop-app issue. Microsoft maps this failure to response code 540415 and describes it as a case where the SBC offer is missing or the request carries an unsupported media type. That changes the whole troubleshooting path: the first place to read is normally the SIP INVITE, its headers, and its body on the SBC side. [✅Source-1]

Table of Contents

What Error Code 415 Means

Error Code 415 is the Teams Phone presentation of a SIP Unsupported Media Type condition. Engineers often compare cases like this with other documented Microsoft Teams Direct Routing and media negotiation error codes to determine whether the rejection belongs to message structure, codec negotiation, or SBC signaling behavior. In plain language, the call setup message reached a stage where Teams could not use the media declaration it received. Sometimes the body is missing. Sometimes the declared content type does not match what the service expects. Sometimes the message carries material that does not belong in that offer at all.

That is why broad client-side actions such as cache clearing, profile resets, or reinstalling the app often miss the mark here. The visible symptom appears on the user side. The actual defect usually lives in the signaling payload built by the SBC, the interop template, or a route-specific message rewrite. On the wire sits the answer.

Signals Worth Reading Before You Change Anything

Teams publishes two values that matter here: the SIP response code and the Microsoft response code. Microsoft also explains a simple but very useful prefix rule: if the Microsoft response code starts with 560, the final SIP response came from the SBC; other prefixes mean the final response was generated by a Microsoft service. For 540415, the service-side explanation is already published. [✅Source-2]

Field	Value You May See	What It Tells You
SIP Response Code	415	The request body or offer was rejected as an unsupported media type.
Microsoft Response Code	540415	Microsoft ties this failure to a missing SBC offer or unsupported media type.
Prefix Check	560xxx vs non-560xxx	560xxx points first to the SBC side; non-560 prefixes point first to Microsoft-generated final SIP handling.
Reporting Location	Teams admin center, QER/PSTN reporting	You can confirm whether the fault is isolated, recurring, or widespread before changing routing objects.

Where the Call Fails in Practice

Teams Phone Direct Routing does not start with the INVITE. It starts with TLS and SIP OPTIONS. Microsoft’s documented flow is straightforward: the SBC opens a TLS connection to the SIP proxy, presents its certificate, sends OPTIONS, and receives 200 OK when the proxy recognizes the tenant and the SBC is healthy. If the request is not valid, the TLS connection can be closed before normal health signaling settles. [✅Source-3]

1. The SBC initiates TLS to the Teams SIP proxy and presents its certificate.
2. If the connection checks pass, the SBC sends OPTIONS and the proxy returns 200 OK.
3. The SBC is then shown as Active in the Teams admin center.
4. Only after that transport and health layer is working does the actual call setup message get processed.

A trunk can therefore look healthy and still fail with 415 when the real call offer arrives. Transport health and INVITE content quality are not the same check. Often mixed up, they are.

What to Review in the SIP Headers Before You Touch Voice Routes

Microsoft’s SIP protocol documentation adds a layer many short articles miss. For incoming Direct Routing messages, the Contact header must use the paired SBC FQDN, that FQDN must match the certificate CN or SAN, supported wildcards are allowed in the documented pattern, and SIPS URI is not supported in this path. Microsoft also states that if the Contact host is sent as an IP address instead of an FQDN, the connection is refused with 403. [✅Source-4]

• Contact header: confirm it carries the paired SBC FQDN, not a bare IP.
• Certificate alignment: confirm the FQDN in signaling matches the certificate CN or SAN exactly, or matches the documented wildcard pattern.
• Tenant mapping: confirm the FQDN belongs to a Microsoft 365 tenant that Teams can resolve correctly.
• URI format: remove unsupported SIP shapes before chasing route policies.

This section matters because a bad header set can steer troubleshooting in the wrong direction. The body may still be wrong, yes, but header identity errors create different failure patterns. Reading those patterns early saves a lot of needless route editing.

What to Review in the SDP Body and Media Offer

The SDP body deserves line-by-line attention. Microsoft documents the supported codec set on the leg between the SBC and Teams media handling as SILK, G.711, G.722, and G.729. That does not mean every 415 is a codec issue. It does mean the codec list and the message body belong in the same inspection pass. [✅Source-5]

1. Confirm the INVITE body exists. Empty, truncated, or malformed bodies can stop setup early.
2. Confirm the declared content matches the body. A clean SDP body must align with the message declaration.
3. Review codec offers. Make sure at least one supported codec is present on the SBC side of the call path.
4. Compare working and failing calls. Same SBC, same trunk, same software family. That comparison reveals template drift very quickly.
5. Remove extras that do not belong. Interop features sometimes inject fields or body parts that are harmless elsewhere and rejected here.

When a working call and a failed call differ only in CONTENT-TYPE, the SDP payload, or the offer structure, you usually have enough evidence to correct the SBC template without guessing. Guessing is expensive. Packet truth is cheaper.

How to Narrow the Scope

Use Tenant Reporting Before You Edit Live Configuration

Microsoft’s PSTN reporting for Teams lets you review 7-day, 30-day, and 180-day windows and break the data down by call type, SBC, and country or region. It also surfaces service usage, attempt calls, connected calls, concurrent calls, active users, and end-reason patterns. For a 415 investigation, that makes one question easy to answer: is this a tenant-wide fault, a single-trunk fault, or a recent regression on one route? [✅Source-6]

• Only one SBC affected: look first at that SBC’s rewrite rules, firmware behavior, or trunk template.
• Only one country or route affected: translation and carrier-facing normalization become more likely.
• Sudden spike after a quiet period: change windows, firmware changes, certificate replacement, or route edits deserve attention.

For Larger Environments, Pull Raw Direct Routing Logs

Microsoft Graph also exposes Direct Routing call records. The published API returns a log of direct routing calls, gives a 200 OK on success, and paginates after 1,000 entries with an @odata.nextLink for the next page. That is useful when you need a sharper cut by time range, call volume, or automation. [✅Source-7]

For busy tenants, this is often the cleanest way to prove whether 415 tracks one SBC, one number range, one time window, or one deployment change. Once that pattern is clear, troubleshooting gets smaller. Much smaller.

When Vendor Escalation Makes Sense

Microsoft states that Direct Routing support is tied to certified SBCs, and certification is granted to specific firmware families. Microsoft also states that support for SBC-related issues flows through the certified SBC vendor first. That matters for 415 cases because many fixes live in vendor templates, firmware behavior, or product-specific SIP manipulation features rather than in Teams policies alone. [✅Source-8]

1. You already confirmed the SBC is Active and transport health is stable.
2. You already checked Contact header, certificate alignment, CONTENT-TYPE, and SDP structure.
3. You already compared a working INVITE and a failing INVITE.
4. The issue still reproduces on the same certified SBC path.

At that point, vendor escalation is not overkill. It is the right next move. Especially when the failing message is being generated by a device template you did not write by hand.

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FAQ

Is Error Code 415 a Teams desktop app problem?

Usually no. In Teams Phone Direct Routing, this error points first to the SIP message body, the SBC offer, or the media declaration rather than to the local app cache.

What does Microsoft response code 540415 mean?

It is Microsoft’s published mapping for this 415 scenario. The documented meaning is that the SBC offer is missing or that the request contains an unsupported media type.

Can an SBC be active and still produce 415 failures?

Yes. Active status mainly tells you that TLS and OPTIONS health checks are working. The later INVITE can still fail if its headers, content type, or SDP body are not acceptable.

Which part of the trace should be compared first?

Compare a working INVITE and a failing INVITE from the same SBC. Read the Contact header, CONTENT-TYPE, SDP body, and offered codecs in that order.

Does codec cleanup matter when the visible error is 415?

Yes. Not every 415 is a codec-only problem, but the supported codec list on the SBC side is limited, so codec offers and SDP formatting should be reviewed together.

How can you prove whether the issue is isolated or widespread?

Use Teams PSTN reporting to review 7-day, 30-day, and 180-day patterns by SBC, geography, and call type. For high-volume analysis, use Direct Routing call records through Microsoft Graph.