diff --git a/app/controllers/api/messaging.php b/app/controllers/api/messaging.php
index 10369bc00..a76c4909c 100644
--- a/app/controllers/api/messaging.php
+++ b/app/controllers/api/messaging.php
@@ -2596,7 +2596,7 @@ App::post('/v1/messaging/messages/email')
     ->param('targets', [], new ArrayList(new UID()), 'List of Targets IDs.', true)
     ->param('cc', [], new ArrayList(new UID()), 'Array of target IDs to be added as CC.', true)
     ->param('bcc', [], new ArrayList(new UID()), 'Array of target IDs to be added as BCC.', true)
-    ->param('attachments', [], new ArrayList(new CompoundUID()), 'Array of compound bucket IDs to file IDs to be attached to the email.', true)
+    ->param('attachments', [], new ArrayList(new CompoundUID()), 'Array of compound ID strings of bucket IDs and file IDs to be attached to the email. They should be formatted as <BUCKET_ID>:<FILE_ID>.', true)
     ->param('status', MessageStatus::DRAFT, new WhiteList([MessageStatus::DRAFT, MessageStatus::SCHEDULED, MessageStatus::PROCESSING]), 'Message Status. Value must be one of: ' . implode(', ', [MessageStatus::DRAFT, MessageStatus::SCHEDULED, MessageStatus::PROCESSING]) . '.', true)
     ->param('html', false, new Boolean(), 'Is content of type HTML', true)
     ->param('scheduledAt', null, new DatetimeValidator(requireDateInFuture: true), 'Scheduled delivery time for message in [ISO 8601](https://www.iso.org/iso-8601-date-and-time-format.html) format. DateTime value must be in future.', true)