Synapseのhomeserver.ymlの設定変更が必要です。

@@ -944,7 +954,7 @@ media_store_path: "/data/media_store"
 # 'false' by default: uncomment the following to enable it (and specify a
 # url_preview_ip_range_blacklist blacklist).
 #
-#url_preview_enabled: true
+url_preview_enabled: true

 # List of IP address CIDR ranges that the URL preview spider is denied
 # from accessing.  There are no defaults: you must explicitly
@@ -960,26 +970,26 @@ media_store_path: "/data/media_store"
 # This must be specified if url_preview_enabled is set. It is recommended that
 # you uncomment the following list as a starting point.
 #
-#url_preview_ip_range_blacklist:
-#  - '127.0.0.0/8'
-#  - '10.0.0.0/8'
-#  - '172.16.0.0/12'
-#  - '192.168.0.0/16'
-#  - '100.64.0.0/10'
-#  - '192.0.0.0/24'
-#  - '169.254.0.0/16'
-#  - '192.88.99.0/24'
-#  - '198.18.0.0/15'
-#  - '192.0.2.0/24'
-#  - '198.51.100.0/24'
-#  - '203.0.113.0/24'
-#  - '224.0.0.0/4'
-#  - '::1/128'
-#  - 'fe80::/10'
-#  - 'fc00::/7'
-#  - '2001:db8::/32'
-#  - 'ff00::/8'
-#  - 'fec0::/10'
+url_preview_ip_range_blacklist:
+  - '127.0.0.0/8'
+  - '10.0.0.0/8'
+  - '172.16.0.0/12'
+  - '192.168.0.0/16'
+  - '100.64.0.0/10'
+  - '192.0.0.0/24'
+  - '169.254.0.0/16'
+  - '192.88.99.0/24'
+  - '198.18.0.0/15'
+  - '192.0.2.0/24'
+  - '198.51.100.0/24'
+  - '203.0.113.0/24'
+  - '224.0.0.0/4'
+  - '::1/128'
+  - 'fe80::/10'
+  - 'fc00::/7'
+  - '2001:db8::/32'
+  - 'ff00::/8'
+  - 'fec0::/10'

 # List of IP address CIDR ranges that the URL preview spider is allowed
 # to access even if they are specified in url_preview_ip_range_blacklist.
@@ -1044,13 +1054,14 @@ media_store_path: "/data/media_store"
 #
 # Example:
 #
-# url_preview_accept_language:
-#   - en-UK
-#   - en-US;q=0.9
-#   - fr;q=0.8
-#   - *;q=0.7
-#
+
 url_preview_accept_language:
+  - "ja-JP;q=0.9"
+  - "en-US;q=0.8"
+  - "*;q=0.7"
+
+#
+# url_preview_accept_language:
 #   - en