diff --git a/nmcp-tasks/src/main/kotlin/nmcp/internal/task/metadata.kt b/nmcp-tasks/src/main/kotlin/nmcp/internal/task/metadata.kt
index a78a5dc..1f40a12 100644
--- a/nmcp-tasks/src/main/kotlin/nmcp/internal/task/metadata.kt
+++ b/nmcp-tasks/src/main/kotlin/nmcp/internal/task/metadata.kt
@@ -2,10 +2,10 @@ package nmcp.internal.task
 
 import kotlinx.serialization.Serializable
 import kotlinx.serialization.StringFormat
-import nl.adaptivity.xmlutil.serialization.XML
+import nl.adaptivity.xmlutil.XmlDeclMode
+import nl.adaptivity.xmlutil.core.XmlVersion
 import nl.adaptivity.xmlutil.serialization.XML1_0
 import nl.adaptivity.xmlutil.serialization.XmlChildrenName
-import nl.adaptivity.xmlutil.serialization.XmlConfig
 import nl.adaptivity.xmlutil.serialization.XmlElement
 import nl.adaptivity.xmlutil.serialization.XmlSerialName
 
@@ -84,4 +84,9 @@ internal data class ArtifactMetadata(
 
 internal val xml: StringFormat = XML1_0.recommended {
     indentString = "  "
+    // Maven Central doesn't understand XML 1.1
+    // See also https://github.com/pdvrieze/xmlutil/issues/324
+    xmlVersion = XmlVersion.XML10
+    // Also set the charset explicitly
+    xmlDeclMode = XmlDeclMode.Charset
 }
diff --git a/nmcp-tasks/src/main/kotlin/nmcp/transport/transport.kt b/nmcp-tasks/src/main/kotlin/nmcp/transport/transport.kt
index 1ee986f..f82850d 100644
--- a/nmcp-tasks/src/main/kotlin/nmcp/transport/transport.kt
+++ b/nmcp-tasks/src/main/kotlin/nmcp/transport/transport.kt
@@ -101,7 +101,7 @@ internal class HttpTransport(
             response.close()
             return null
         }
-        if(!response.isSuccessful) {
+        if (!response.isSuccessful) {
             response.close()
             error("Nmcp: cannot GET '$url' (statusCode=${response.code}):\n${response.body.string()}")
         }
@@ -127,31 +127,24 @@ internal class HttpTransport(
                 check(response.isSuccessful) {
                     buildString {
                         appendLine("Nmcp: cannot PUT '$url' (statusCode=${response.code}).")
-                        appendLine("Response body: ${response.body.string()}")
+                        appendLine("Response body: '${response.body.string()}'")
                         when (response.code) {
+                            400 -> {
+                                appendLine("Things to double check:")
+                                appendLine("Your artifacts have proper extensions (.jar, .pom, ...).")
+                                appendLine("If publishing a XML file, the XML version is 1.0.")
+                                appendLine("If publishing a snapshot, the artifacts version is ending with `-SNAPSHOT`.")
+                            }
+                            401 -> {
+                                appendLine("Check your credentials")
+                                appendLine("If publishing a snapshot, make sure you enabled snapshots on your namespace at https://central.sonatype.com/publishing/namespaces.")
+                            }
+                            403 -> {
+                                appendLine("Check that you are publishing to the correct groupId.")
+                            }
                             429 -> {
                                 appendLine("Too many requests, try again later")
                             }
-                            else -> {
-                                appendLine("Things to double check:")
-                                /**
-                                 * I have seen 401 for this
-                                 */
-                                appendLine(" - Are your credentials correct?")
-                                appendLine(" - Did you enable the snapshots on your namespace at https://central.sonatype.com/publishing/namespaces?")
-                                /**
-                                 * I have seen 400 for this
-                                 */
-                                appendLine(" - Is your version ending with `-SNAPSHOT`?")
-                                /**
-                                 * I have seen 400 for this.
-                                 */
-                                appendLine(" - Do your artifacts have proper extensions (.jar, .pom, ...)?")
-                                /**
-                                 * I have seen 403 for this.
-                                 */
-                                appendLine(" - Is your groupId correct?")
-                            }
                         }
                     }
                 }
diff --git a/nmcp-tasks/src/test/kotlin/MetadataTest.kt b/nmcp-tasks/src/test/kotlin/MetadataTest.kt
index 314e644..393e532 100644
--- a/nmcp-tasks/src/test/kotlin/MetadataTest.kt
+++ b/nmcp-tasks/src/test/kotlin/MetadataTest.kt
@@ -45,7 +45,7 @@ class MetadataTest {
          */
         // language=xml
         val xmlData = """
-            <?xml version='1.1' ?>
+            <?xml version='1.0' encoding='UTF-8' ?>
             <metadata modelVersion="1.1.0">
               <groupId>com.apollographql.apollo</groupId>
               <artifactId>apollo-api-jvm</artifactId>
@@ -111,7 +111,7 @@ class MetadataTest {
     fun versionMetadataIsEncodedSuccessfully() {
         // language=xml
         val xmlData = """
-            <?xml version='1.1' ?>
+            <?xml version='1.0' encoding='UTF-8' ?>
             <metadata modelVersion="1.1.0">
               <groupId>com.apollographql.apollo</groupId>
               <artifactId>apollo-api-jvm</artifactId>
@@ -178,7 +178,7 @@ class MetadataTest {
 
         val result = encodeToXml(metadata)
 
-        assertEquals(xmlData, result,)
+        assertEquals(xmlData, result)
     }
 
     @Test