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SurveyJS
Open-Source JSON Form Builder to Create Dynamic Forms Right in Your App. With SurveyJS form UI libraries, you can build and style forms in a fully-integrated drag & drop form builder, render them in your JS app, and store form submission data in any backend, inc. PHP, ASP.NET Core, and Node.js.
After a quick look (https://developer.twitter.com/en/docs/twitter-api) I imagine they're basically talking about making those offers paid. OAuth is another kind of API they wouldn't have interest in changing. Especially since you need to get a token in the first place in order to determine if you're elegible to make paid requests. And it's easy to get around request origin whitelisting, which is the only real way you could make paid oauth I imagine?