The "Ballot Type" field in the Ballot Tracker is used internally by the County Elections Office to record how your application was received. It refers to your application for a mail-in ballot, and not the mail-in ballot you returned. If you already received your mail-in ballot, or a notice that your application was approved, this issue has already been resolved at the Elections Office.
So, what does it mean? "Not verified" means that when your application was received, it could not be verified by the State's automatic matching process which uses your PA drivers license record to verify your identity. Applications that use the last 4 digits of a voter's Social Security Number instead of a PA Driver's license or PennDOT ID number can't be verified using this automated system. And sometimes the punctuation, hyphenation, or spelling on a voter's application is slightly different than it appears on their PA Driver's license or PennDOT ID. (For example, "Phil" instead of "Philip," or "St" instead of "Street", misspelling the name of your county...)
Your County Elections Division resolves these issues BEFORE your application is approved and your ballot is sent to you. If they cannot resolve the issue, they send the voter a letter, requesting further information.