diff --git a/src/adcp/compat/legacy/v2_5/_media_buy_helpers.py b/src/adcp/compat/legacy/v2_5/_media_buy_helpers.py
index cb49f206..3d6b361c 100644
--- a/src/adcp/compat/legacy/v2_5/_media_buy_helpers.py
+++ b/src/adcp/compat/legacy/v2_5/_media_buy_helpers.py
@@ -14,17 +14,22 @@
 
 from typing import Any
 
-from adcp.compat.legacy.v2_5._url import strip_url_scheme
+from adcp.compat.legacy.v2_5._url import extract_brand_domain
 
 
 def adapt_brand_manifest_to_brand(payload: dict[str, Any]) -> dict[str, Any]:
     """Rewrite v2.5 ``brand_manifest`` (URL string) to v3 ``brand``
-    ``{domain: ...}``. Caller-supplied ``brand`` wins when both fields
-    are present (half-migrated buyer)."""
+    ``{domain: ...}``.  Caller-supplied ``brand`` wins when both fields
+    are present (half-migrated buyer).
+
+    Uses ``extract_brand_domain`` to isolate the hostname from full URLs
+    (e.g. ``"https://acme.com/.well-known/brand.json"`` → ``"acme.com"``)
+    so the result satisfies ``BrandReference.domain``'s hostname-only regex.
+    """
     out = dict(payload)
     manifest = out.pop("brand_manifest", None)
     if isinstance(manifest, str) and manifest and "brand" not in out:
-        out["brand"] = {"domain": strip_url_scheme(manifest)}
+        out["brand"] = {"domain": extract_brand_domain(manifest)}
     return out
 
 
diff --git a/src/adcp/compat/legacy/v2_5/_url.py b/src/adcp/compat/legacy/v2_5/_url.py
index 23aa913b..1c2e0f09 100644
--- a/src/adcp/compat/legacy/v2_5/_url.py
+++ b/src/adcp/compat/legacy/v2_5/_url.py
@@ -8,6 +8,8 @@
 
 from __future__ import annotations
 
+from urllib.parse import urlparse
+
 
 def strip_url_scheme(url: str) -> str:
     """``https://acme.example.com/`` → ``acme.example.com``.
@@ -16,6 +18,10 @@ def strip_url_scheme(url: str) -> str:
     after trailing-slash strip), ``http://`` schemes (legacy clients
     don't all enforce https), and trailing slashes from sloppy
     concatenation.
+
+    Does NOT strip URL paths or ports.  Use ``extract_brand_domain``
+    when the input may be a full URL (scheme + path) and you need only
+    the hostname component.
     """
     s = url.strip()
     for prefix in ("https://", "http://"):
@@ -23,3 +29,41 @@ def strip_url_scheme(url: str) -> str:
             s = s[len(prefix) :]
             break
     return s.rstrip("/")
+
+
+def extract_brand_domain(url: str) -> str:
+    """Extract a ``BrandReference.domain``-safe hostname from a brand_manifest URL.
+
+    v2.5 ``brand_manifest`` is documented as a URL to a JSON file
+    (e.g. ``"https://acme.com/.well-known/brand.json"``).  The v3
+    ``BrandReference.domain`` field requires a bare hostname matching
+    ``^[a-z0-9]([a-z0-9-]*[a-z0-9])?(\\.[a-z0-9]([a-z0-9-]*[a-z0-9])?)*$``.
+
+    Behaviour by input shape:
+
+    * Full URL with scheme (``https://acme.com/path``):
+      ``urlparse`` extracts the hostname (``"acme.com"``); path and
+      port are discarded.  Uppercase schemes are normalised by
+      ``urlparse``; uppercase hostnames are lowercased by ``urlparse``
+      (e.g. ``HTTPS://ACME.COM/path`` → ``"acme.com"``).
+    * URL with port (``https://acme.com:8443/path``):
+      hostname is extracted without the port (``"acme.com"``).
+    * Bare domain without scheme (``acme.com``):
+      ``urlparse`` returns ``hostname=None``; falls back to
+      ``strip_url_scheme`` which returns the input unchanged after
+      stripping any trailing slashes.
+    * IPv6 literal (``https://[::1]/path``):
+      ``urlparse`` returns ``hostname="::1"`` (brackets stripped).
+      This value does not satisfy ``BrandReference.domain``'s regex;
+      callers must validate the result if IPv6 addresses are possible.
+
+    The caller is responsible for ensuring ``url`` is non-empty before
+    calling (both adapter call sites already gate on
+    ``isinstance(manifest, str) and manifest``).
+    """
+    s = url.strip()
+    # urlparse correctly handles full URLs: extracts hostname, drops path and port.
+    # For bare domains (no scheme), urlparse treats the input as a path-only URI
+    # and returns hostname=None, so we fall back to strip_url_scheme.
+    hostname = urlparse(s).hostname
+    return hostname if hostname is not None else strip_url_scheme(s)
diff --git a/src/adcp/compat/legacy/v2_5/get_products.py b/src/adcp/compat/legacy/v2_5/get_products.py
index 2ea88ce2..caf37fed 100644
--- a/src/adcp/compat/legacy/v2_5/get_products.py
+++ b/src/adcp/compat/legacy/v2_5/get_products.py
@@ -40,7 +40,7 @@
 
 from adcp.compat.legacy import register_adapter
 from adcp.compat.legacy.types import AdapterPair
-from adcp.compat.legacy.v2_5._url import strip_url_scheme
+from adcp.compat.legacy.v2_5._url import extract_brand_domain
 
 # v2.5 channel buckets to v3 channel slugs. Multi-mapped buckets resolve
 # to all listed v3 channels; downstream consumers can narrow further via
@@ -127,10 +127,14 @@ def adapt_request(payload: dict[str, Any]) -> dict[str, Any]:
     """Translate a v2.5 ``get_products`` request to v3 shape."""
     out = dict(payload)
 
-    # brand_manifest (v2.5 URL string) → brand.domain (v3 BrandReference)
+    # brand_manifest (v2.5 URL string) → brand.domain (v3 BrandReference).
+    # v2.5 spec documents brand_manifest as a URL to a JSON file, so paths
+    # are the expected input shape.  extract_brand_domain uses urlparse to
+    # isolate the hostname so the result satisfies BrandReference.domain's
+    # hostname-only regex.
     brand_manifest = out.pop("brand_manifest", None)
     if isinstance(brand_manifest, str) and brand_manifest and "brand" not in out:
-        out["brand"] = {"domain": strip_url_scheme(brand_manifest)}
+        out["brand"] = {"domain": extract_brand_domain(brand_manifest)}
 
     # promoted_offerings → catalog
     promoted = out.pop("promoted_offerings", None)
diff --git a/tests/test_legacy_adapter_v2_5_get_products.py b/tests/test_legacy_adapter_v2_5_get_products.py
index 7fa873dd..71ace69a 100644
--- a/tests/test_legacy_adapter_v2_5_get_products.py
+++ b/tests/test_legacy_adapter_v2_5_get_products.py
@@ -57,6 +57,20 @@ def test_brand_manifest_strips_trailing_slash() -> None:
     assert out["brand"] == {"domain": "acme.example.com"}
 
 
+def test_brand_manifest_with_path_extracts_hostname() -> None:
+    """Regression for #677: brand_manifest URL with a path must extract only
+    the hostname so the result satisfies BrandReference.domain's regex."""
+    out = _adapt({"brand_manifest": "https://acme.com/.well-known/brand.json"})
+    assert out["brand"] == {"domain": "acme.com"}
+    assert "brand_manifest" not in out
+
+
+def test_brand_manifest_with_port_drops_port() -> None:
+    """Port numbers are stripped; only the hostname reaches brand.domain."""
+    out = _adapt({"brand_manifest": "https://acme.com:8443/.well-known/brand.json"})
+    assert out["brand"] == {"domain": "acme.com"}
+
+
 def test_brand_field_takes_precedence_over_manifest() -> None:
     """Half-migrated buyer sends both — keep the v3 field."""
     out = _adapt(
diff --git a/tests/test_legacy_adapter_v2_5_media_buy.py b/tests/test_legacy_adapter_v2_5_media_buy.py
index 872f8974..d96062c3 100644
--- a/tests/test_legacy_adapter_v2_5_media_buy.py
+++ b/tests/test_legacy_adapter_v2_5_media_buy.py
@@ -44,6 +44,20 @@ def test_create_media_buy_brand_manifest_becomes_brand_domain() -> None:
     assert "brand_manifest" not in out
 
 
+def test_create_media_buy_brand_manifest_with_path_extracts_hostname() -> None:
+    """Regression for #677: brand_manifest URL with a path must extract only
+    the hostname so the result satisfies BrandReference.domain's regex."""
+    out = v2_5_cmb.adapt_request({"brand_manifest": "https://acme.com/.well-known/brand.json"})
+    assert out["brand"] == {"domain": "acme.com"}
+    assert "brand_manifest" not in out
+
+
+def test_create_media_buy_brand_manifest_with_port_drops_port() -> None:
+    """Port numbers are stripped; only the hostname reaches brand.domain."""
+    out = v2_5_cmb.adapt_request({"brand_manifest": "https://acme.com:8443/.well-known/brand.json"})
+    assert out["brand"] == {"domain": "acme.com"}
+
+
 def test_create_media_buy_brand_wins_over_manifest_when_both_present() -> None:
     out = v2_5_cmb.adapt_request(
         {