A Verification of Non-Filing Letter means the IRS hasn't received a 1040 for the year in question. Please see this link for more details on the IRS transcript status.
However, you mention that your tax return was filed and accepted. I recommend checking your e-file status using these steps. If you are due a refund from the IRS, there is also a place in the previous link you can also use to track your refund.
If you're return does show it was successfully e-filed and accepted, it may just be the IRS taking a bit longer to updates the transcript records.