docs: Add warning that email attachments are temporarily unavailable

contents/docs/workflows/transactional-emails/api.mdx

@@ -323,6 +323,12 @@ $result = PostHog::emails()->send([
 
 ### Copies and attachments
 
+<CalloutBox icon="IconWarning" title="Attachments are temporarily unavailable" type="warning">
+
+A send with `attachments` gets a `400` error with the code `invalid_request`, and `attr` is `attachments`. PostHog sends nothing. Leave out `attachments` to send the email. `cc` and `bcc` work as described below.
+
+</CalloutBox>
+
 Content from your code also takes these fields. A template send takes none of them, because the template uses its own settings.
 
 | Field | Required | Description |

contents/docs/workflows/transactional-emails/examples.mdx

@@ -155,6 +155,12 @@ Without a distinct ID, PostHog records the email on a person whose distinct ID i
 
 ## Receipt with a PDF
 
+<CalloutBox icon="IconWarning" title="Attachments are temporarily unavailable" type="warning">
+
+This example gets a `400` error while attachments are unavailable. To send the receipt now, leave out `attachments`. The `cc` copy still works.
+
+</CalloutBox>
+
 Send a receipt with the invoice attached, and a copy to the customer's billing contact. Attachments and copies work only with [content from your code](/docs/workflows/transactional-emails#choose-where-the-emails-content-lives), so your code renders the email. The SDKs don't send copies and attachments yet, so this example uses the API.
 
 | Setting | Value |

contents/docs/workflows/transactional-emails/index.mdx

@@ -90,7 +90,7 @@ You can write the email in PostHog, or send content that your code renders. Both
 | Who edits it | Anyone on your team, in the PostHog editor, with no deploy | Engineers, in your codebase |
 | Best for | Copy that changes often, and teams that want drafts, versions, and a preview | [React Email](https://react.email) or other templates that you already have, and a move from another email provider |
 | What a send carries | `template_id` and the template's variables | `template_key`, `subject`, and `html` or `text` |
-| Copies and attachments | Not on the send | `cc`, `bcc`, and `attachments`, on the API |
+| Copies and attachments | Not on the send | `cc` and `bcc`, on the API. Attachments are [temporarily unavailable](/docs/workflows/transactional-emails/api#copies-and-attachments). |
 
 The rest of this page covers emails that you write in PostHog. For content from your code, see your SDK's page or [the API](/docs/workflows/transactional-emails/api#send-content-from-your-code).