If you did not receive an email from TurboTax showing the extension was rejected, then it was accepted by the IRS.
See this TurboTax support FAQ for checking the status of an e-file - https://ttlc.intuit.com/community/return-status/help/how-do-i-check-my-e-file-status/01/25538
I suggest that you apply the words “Accepted” or “Rejected” after a client submits their Tax Extension. Not indicating any verbage to me is Unacceptable. I tried & tried to repeatedly submit this extension only to give up after Midnite of the 15th when it was due. I ended up paying $19.95 to another Tax agency who ensured my extension would go thru immediately & it did! Not only that but they have followed up with me in email form since then. I have used Turbo Tax for years & have done Tax Extensions thru them a number of times without problems. I am very disappointed in them right now!!! 🥴