Web-to-Lead Testing in Sandbox Not Recognizing Instance Number

Hi everyone,

I'm encountering an issue while testing a web-to-lead form in my sandbox. After updating the form's action URL to reflect my sandbox instance (e.g., CAN3V), I'm getting the following error:

“can3v.salesforce.com’s server IP address could not be found.”

I can log in to my sandbox without any issues, and the instance number (CAN3V) is confirmed. In addition to updating the instance number in the form's action URL, I’ve also replaced all the Org ID's in the HTML with the correct ones from my sandbox environment.

Am I missing something, or is there another reason why this error might be occurring?

Any insights would be greatly appreciated!

Thanks in advance,

Thomas