Attach a file from an order or customer metafield

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Send the PDF another app saved on an order or customer metafield as an email attachment from Shopify Flow: setup, permissions, file names, empty metafields and limits.

Many apps save a file on the order or the customer: an invoice or packing slip PDF from an invoicing app, a certificate, a signed contract. Shopify stores it in a metafield, either as a file in your Shopify Files or as a link to the file. This app can attach that file to the email a Flow workflow sends, without you uploading or linking anything by hand.

How it works

Another app (or you) writes the file, or a link to it, into a metafield of the order or customer. In your Shopify admin that is Settings > Custom data > Orders (or Customers): a definition of type File, URL, or a text field an app writes a link into.
In an email layout you add an attachment and choose Metafield as its source, then pick that definition. The picker shows what each one holds: a file, a link, or a list of either.
In Shopify Flow, the Send Transactional Email or Send Marketing Email step has an Order field and a Customer field. Flow fills them from the trigger, so a workflow started by Order created already knows which order.
When the email is sent, the app reads that metafield on that order or customer, downloads the file (from your Shopify Files, or from the link), and attaches it. A list metafield attaches every entry.

The layout only names the metafield. The workflow says whose order or customer, so one layout serves every order.

A freshly added Send Transactional Email step in Shopify Flow with its Order field set to order.id and its Customer field to order.customer.id, above the To, CC and BCC fields — The step in Shopify Flow: Order and Customer are filled from the trigger, here an order workflow. A step added before 1.17 does not have them; delete it and add it again.

Files and links

The metafield holds	Definition type	What the app does
A Shopify file	File, List of files	Follows the reference to the file in your Files and downloads it
A link	URL, List of URLs, or a text field	Downloads the file from that link. Only `https://` links work; a link that does not answer or points at something other than a PDF, image, CSV or text file fails the send with the reason

Either way the size is checked when the email is sent, not in the editor, so metafield attachments are not counted in the editor's attachment total.

Set it up

Rich text and HTML layouts

In the Attachments card at the bottom of the editor, click Add from metafield. Pick Order or Customer, then the definition. The row shows the definition's name, what it holds and its namespace.key; Change picks another one.

The Attachments card of a rich text layout with the buttons Add attachment, Add from URL and Add from metafield — The Attachments card of a rich text or HTML layout: Add from metafield next to the upload and URL buttons.

Visual layouts

Add an Attachment block (or open one) and switch its source to Metafield. Choose metafield opens the same picker.

An attachment block in the visual builder with its source switched to Metafield, the Choose metafield button, the file name override and the Optional checkbox — The attachment block with Metafield as its source: choose the definition, override the file name, and decide whether an empty metafield holds the email back.

The dialog Attach a file from a metafield with Order chosen as the resource and the definitions Invoice PDF (File) and Invoice URL (Link) listed below a search field — The picker: Order or Customer first, then the definitions of that resource, each with what it holds. Invoice PDF is selected.

The attachment block after choosing the metafield: Invoice PDF, File, Order custom.invoice_pdf, a Change metafield button, the file name override and the Optional checkbox — The block after the choice: the definition's name, what it holds and its namespace.key. Change metafield picks another one.

The permission

The app is installed without any access to your store data. The first time you pick an order or customer metafield, the picker asks for permission to read that resource's metafields and the files they point to. Shopify shows its own consent dialog; after Update, the list of definitions loads.

You can review and withdraw every permission at any time on the app's Permissions page. Withdrawing one makes every email that attaches a file from such a metafield fail until it is granted again. What each permission reads, and what it does not, is on Permissions: what the app can read from your store.

The Permissions page listing Orders and Files as Granted with Revoke buttons, and Customers and Discounts as Not granted with Grant buttons, each with its scope — The Permissions page: every optional permission with its scope, granted or not, and a button to grant or revoke it. Here Orders and Files were granted from the picker.

File name

By default the attachment keeps the file's own name: the name in your Shopify Files, or the last part of the link. The File name field overrides it and supports Liquid, for example invoice-{{ variables.order_name }}.pdf. When a list metafield holds several entries, the second and following get -2, -3 appended to the override.

When the metafield is empty

The app that writes the file often runs a few seconds after the trigger, so at the moment the email step runs the metafield can still be empty. What happens then depends on the Optional checkbox of the attachment:

Optional	Behaviour
Off (default)	The email is not sent yet. The app tells Flow to retry the step, and Flow redelivers it a little later; the email goes out as soon as the file is there.
On	The email is sent without this attachment.

Leave it off for an invoice that must be there. Turn it on for a file that only some orders have.

Requirements and limits

The Flow step needs its Order or Customer field set. Steps that were added before this release do not have the fields yet: delete the step in the Flow editor and add it again.
Files up to 10 MB each; PDF, images, CSV, plain text and calendar files. Videos and 3D models are skipped.
Links must start with https:// and answer without a login. A link that redirects to a non-https address, or into a private network, is refused.
Orders of the last 60 days. Shopify only lets apps read recent orders. For a workflow on an older order the send fails with a clear message.
Microsoft 365 rejects messages with more than 4 MB of attachments in total; see Attachments and images.

What you see in History

Every outcome is on the History page. A step without an order, a withdrawn permission, an order Shopify cannot find, a link that does not answer, or a file over the limit is recorded as Failed with the reason and what to change. An empty metafield with Optional off is not a failure: Flow shows the retries, and the send appears once the file is there. A Resend from History reads the same order or customer again.

A History event of a Return instructions email whose request data carries the orderId of the order the invoice was read from — An email with an attachment from a metafield in History: the request data records which order was read, so a Resend reads it again.

Test it

Send test email in the layout editor has no order or customer to read from, so it sends without metafield attachments. To test the attachment, run the workflow in Flow on an order that already has the file, or use Run on a Flow test with such an order.

Permissions: what the app can read from your store - what the optional permissions read, and how to withdraw them.
Attachments and images - uploaded attachments, Attach vs Link mode and sizes.
Passing data from Shopify Flow - the step fields and variables.
History and troubleshooting - reading a failed send.