diff --git a/woolist-phplist/includes/class-woolist-api.php b/woolist-phplist/includes/class-woolist-api.php
index 050091b..d33b0f4 100644
--- a/woolist-phplist/includes/class-woolist-api.php
+++ b/woolist-phplist/includes/class-woolist-api.php
@@ -104,12 +104,17 @@ class WooList_API {
 			return new WP_Error( 'woolist_json_error', 'phpList did not return JSON. Check endpoint URL and credentials.' );
 		}
 
-		// phpList signals errors via status=error; message may be in several fields.
+		// phpList signals errors via status=error.
+		// v3 nests the message inside data.message: {"status":"error","data":{"code":0,"message":"..."}}
 		if ( isset( $data['status'] ) && strtolower( $data['status'] ) === 'error' ) {
-			$message = $data['errormessage'] ?? $data['message'] ?? $data['data'] ?? 'Unknown API error';
-			// Also dump the full response so the admin can see exactly what phpList said.
+			if ( is_array( $data['data'] ?? null ) ) {
+				$message = $data['data']['message'] ?? $data['errormessage'] ?? $data['message'] ?? 'Unknown API error';
+			} else {
+				$message = $data['errormessage'] ?? $data['message'] ?? $data['data'] ?? 'Unknown API error';
+			}
+			$message = (string) $message;
 			WooList_Logger::error( 'API error  cmd=' . $cmd . '  message=' . $message . '  full_response=' . wp_json_encode( $data ) );
-			return new WP_Error( 'woolist_api_error', (string) $message );
+			return new WP_Error( 'woolist_api_error', $message );
 		}
 
 		WooList_Logger::debug( 'API call succeeded  cmd=' . $cmd . '  response=' . wp_json_encode( $data ) );
@@ -147,16 +152,25 @@ class WooList_API {
 	/**
 	 * Add a subscriber (by ID) to a phpList list.
 	 *
+	 * phpList REST API v3 accepts both "listid"/"subscriberid" (older) and
+	 * "list_id"/"subscriber_id" (some builds). We send all four so whichever
+	 * naming convention this installation uses will be satisfied.
+	 *
 	 * @param int $list_id       phpList list ID.
 	 * @param int $subscriber_id phpList subscriber ID.
 	 * @return array|WP_Error
 	 */
 	public function list_subscriber_add( int $list_id, int $subscriber_id ) {
+		WooList_Logger::debug(
+			'listSubscriberAdd params  listid=' . $list_id . '  subscriberid=' . $subscriber_id
+		);
 		return $this->call(
 			'listSubscriberAdd',
 			[
 				'listid'       => $list_id,
 				'subscriberid' => $subscriber_id,
+				'list_id'      => $list_id,      // alternate param name used by some v3 builds
+				'subscriber_id' => $subscriber_id, // alternate param name
 			]
 		);
 	}