Hi, I was using NFCNDEFReaderSessionDelegate at first to read and write the cards, but didDetect tags method did not detect any tag because my nfc tag is not pre-formatted, it was calling other delegate methods so I have my NFCNDEFReaderSessionDelegate setup correctly. Hence, I used NFCTagReaderSessionDelegate, didDetect tags method of NFCTagReaderSessionDelegate detected tag and the tag was not pre-formatted. The issue I have been facing is I am not able to write for the first time and getting an error Error Domain=NFCError Code=102 Tag Not NDEF formatted UserInfo={NSLocalizedDescription=Tag Not NDEF formatted}. When I used another app from apple store to write data on the same tag which is not pre-formatted. Using that app, I am able to write the data on that tag. That app was using CoreNFC framework I believe, as it has NFC session alert which seems it was from apple library CoreNFC, so I assume that there must be a way to write the data on unformatted nfc tags. Do I have to use