Filing extension - Transmit my return button not doing anything

Try clearing browser cache and cookies (in your browser settings) and then trying again.  This will often resolve the issue. 

You don’t need to file Form 4868 if you make a payment using the IRS
electronic payment options. 
You can pay all or part of your estimated income tax due and **indicate that the payment is for an extension** using Direct Pay, the Electronic Federal Tax Payment System, or using a credit or debit card. Your extension is then automatically granted and you will receive a confirmation number for your records.

I hope you're on the West Coast.