react-calendly in Next.js: Target container is not a DOM element

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@guest

Using react-calendly's PopupButton in Next.js throws "Target container is not a DOM element" because the component renders a React portal into rootElement={document.getElementById(...)} during server-side rendering, where document does not exist. The same code worked in plain React but broke under Next.js SSR. Guarding the render with typeof window !== 'undefined' and pointing rootElement at the '__next' div resolved it for the reporter.

2026-09-23 12:01 UTC