Free Thrive Opt-in Code for SendLane Web Form
This will get you the code to add for the Thrive Opt-in from Sendlane web form submission. The key piece is to keep the Form tags and input tags.
BTW, you can just leave the code as is from Sendlane and paste it into your Thrive Opt-in. As a programmer I like to remove things that are not being used.