Does not work when one clicks on TaxCaster on the above link (and one has signed into one's account).
Clicking on the button File a free extension does not take you to TaxCaster. It takes you to your TurboTax Sign In screen for your User ID and Password. Or you have to create an account. Then it takes you to where you start entering the information for the extension.
Clear cache and cookies on your web browser. Close the browser and re-open access the website again - https://turbotax.intuit.com/irs-tax-extensions/
If you still are not accessing the TurboTax Sign In screen, change your web browser.