Attach MMS Custom Values to SMS in Sparkforge Workflows

By Sparkforge Support Team ·Last reviewed May 3, 2026

Store an MMS image URL as a custom value, then attach that custom value to the SMS action in a workflow. Stay inside the carrier MMS size limits (0.6-1.5 MB depending on carrier and number type) and use jpeg, png, or gif.

Custom values let you reuse a single MMS image URL across snapshots and workflows. Set the value once, drop it into any SMS action, and the message goes out with the attachment.

Attach a custom value MMS to an SMS

Step 1: Create the custom value URL

Go to Settings → Custom Values → + Add Custom Value and paste the MMS URL.

Step 2: Use the custom value in your workflow

Open the workflow where you want to send the MMS. In the SMS action, attach the custom value as the attachment by copying and pasting the value reference.

Note: MMS size limits are set by the carriers, not Sparkforge. See the carrier table below before picking your image.

Carrier MMS size limits

Carrier	Long code	Toll-free	Short code
AT&T	0.6 MB	0.6 MB	0.6 MB
Sprint	1.4 MB	0.6 MB	1.4 MB
T-Mobile	1.5 MB	0.6 MB	1.0 MB
Verizon	0.675 MB	0.6 MB	1.2 MB

Supported file types

jpeg
png
gif

Troubleshooting

Custom value isn't sending the image

Check the basics in this order:

No spaces in the custom value URL. Test by adding the value to a dummy funnel and previewing the page. If the image renders, the value is good.
The file size is within the carrier limit for the destination number type.
The file type is jpeg, png, or gif.

Frequently Asked Questions

What's the smallest MMS limit I should target?

0.6 MB. AT&T caps every number type at 0.6 MB, and toll-free numbers cap at 0.6 MB across all carriers. Sizing under that gets through anywhere.

Which file types work for MMS in Sparkforge?

jpeg, png, and gif. Other formats won't send.

Why does my custom value not render in the SMS?

Most often the URL has a stray space, the file is too large for the destination carrier, or the file type isn't supported. Test the URL in a funnel preview to confirm it loads.

Can I use the same custom value across multiple workflows?

Yes. That's the point. Set the URL once and reference it from any workflow or snapshot that needs the same MMS attachment.