Unsupported operation: Unsupported file structure. 0x4f44213c, 0x50595443

This usually happens when a wrong file is selected. AuthPass only supports kdbx files. Either created by it’s own or through any other Keepass 2.x client.

If you get these specific byte combination: 0x4f44213c, 0x50595443 it is most certainly an HTML website because this byte sequence corresponds to the following ASCII characters: