Can i send opt ins to an external page?

Hi Noah - you definitely can.

When you have the Page Editor open, if you click on your form, you’ll see the form’s properties open up in the right hand bar. There’s a drop down there that lets you change the form confirmation action from “show form confirmation dialog” to “go to another webpage”. If you switch to the latter, you’ll see a space appear to input the URL of your external page.

Once you save and publish your page, anyone who fills out your form will be taken to that URL instead of seeing the built in form confirmation dialog pop-up.