The Divi Theme's Email Optin module (formerly the "Subscribe" module) makes it easy to sign users up to your Aweber email lists. However, one thing you may notice that you can't do is disable the double opt-in feature, even if you have enabled single opt-in within the list's settings on Aweber's site. Furthermore, you won't find an option for it within Divi itself.
The problem is that, by default, Aweber enforces double opt-in on all registrations made via its API regardless of the list settings. Since Divi uses the Aweber API to process signups, that means they are subject to double opt-in.
Fortunately, there is a possible way round this. You can directly request from Aweber that they allow your API-based (i.e. Divi-based) signups to be single opt-in.
To do so, you can follow this advice from ViralSweep:
As of late November 2014, AWeber has changed this policy, and they will now enable single opt-in through their API on a case by case basis.
So, if you want to have your account and your lists enabled for this, all you have to do is contact AWeber through their online form, or email firstname.lastname@example.org. Tell them you want to enable single opt-in for your lists for use through their API. AWeber will then either approve or deny your request after they review your account.
If all goes well and you're approved, future signups through the Divi Email Optin module will then be single opt-in.