iOS 14 Conflict with Underscores in Subdomain


What’s the problem?

iOS 14 no longer supports underscores in subdomains / hostnames.

What forms are impacted?

Any form with an underscore in the subdomain that is being shared via a mobile browser (Chrome, Safari, etc.) on a device that has been updated to iOS 14.

What is a subdomain?

It’s the part of your form URL that comes before “” (Example:

What are we doing to help?

We are releasing a couple fixes to ease the pain of transitioning your subdomain:

To prevent future problems, our subdomain creation modal will no longer let you use underscores.

To buy you some time to remove the underscore from your subdomain, we will have our system begin interpreting hyphens as underscores in your subdomain. This will allow you to update your form URLs wherever you’ve shared them (link on website, embedded, etc.) by changing the underscores in the URLs to hyphens. You can then reshare them, and they will work properly even though this will not match your account subdomain for now

Only after you have updated all of your shared form URLs should you update your subdomain, which will finalize the subdomain transition.


Updating the account subdomain will automatically update the subdomain of all forms in your Account as well. Once you update your subdomain in Formstack, there is no going back. All your forms will have new URLs with your updated subdomain. If you have forms shared or embedded across any websites, we recommend waiting to update your subdomain until you either:

1. Have taken note of any locations where these URLs/embed codes exist so you can reshare the form after updating your subdomain, or

2. Have updated the subdomain in the already-shared URLs/embed codes so that any hyphens in your subdomain are underscores; and then update your subdomain in your Formstack account.

See the example below:

  • Your subdomain is abc_forms.  You can go ahead and start updating shared URLs using the subdomain abc-forms even though in Formstack, your subdomain is still listed as abc_forms. Formstack will translate the - back to a _ to match the subdomain you have in our system.
  • After you have reshared/embedded all your forms using the new subdomain (abc-forms), go into Formstack and update your subdomain, which will finalize the switch.

My forms aren’t used on mobile browsers. Do I still need to do this?

The short answer is no—but it would be wise to do so anyway. It’s difficult to tell where your end user may end up opening their forms.

Can I use underscores in my URL if they aren't part of the subdomain?
Yes, this only impacts underscores in your subdomain. And our released fixes will only be interpreting hyphens as underscores for the subdomain. EX: Your form url is To manually update this URL so that our system recognizes it without changing your subdomain at the global level, change this URL to Underscores outside of your subdomain should NOT be changed to hyphens.

What happens if somebody takes my subdomain while I'm migrating?
Don't worry, we've prevented anyone from taking the hyphenated version of your current subdomain while you're migrating everything over.

Was this article helpful?
7 out of 8 found this helpful