Start here for answers. If your issue isn't covered, tell us through the feedback page — the book title and the page where the problem appears help most.
Add a WebDAV connection in your library and enter your NAS's WebDAV service address, for example http://192.168.11.100:5005 (on Synology, install and enable WebDAV Server in Package Center first). Add your username and password, and you can browse and open the comic files stored there. When you're away from home, replace the address with your own domain or remote-access address.
For an SMB connection, enter your NAS's LAN address, the share name, and your username and password. DuoComic lists the share's root first, then you navigate to the folder where your comics live. For access away from home, join your home network first (for example with a mesh VPN tool such as Tailscale) and keep using the LAN address.
OPDS is a standard catalog protocol for book libraries. Many library servers (such as Kavita and Komga) give you a catalog URL once OPDS is enabled — usually something like https://your-address/opds. Enter that URL plus your username and password as an OPDS connection in DuoComic to browse, download, and read by catalog. The public Project Gutenberg OPDS catalog at https://www.gutenberg.org/ebooks.opds/ needs no account and is a good way to try the feature.
A 401 means the server asked for sign-in and the credentials were missing or incorrect. Double-check your username and password. Some OPDS services (such as Standard Ebooks) require a membership account and also return 401 when you are not signed in.
CBZ / ZIP, CBR / RAR, PDF, EPUB, and plain image folders. Text-based EPUB books are typeset into pages for reading; comic files support single-page, two-page spread, and vertical scroll modes.
Open any book, tap the center of the screen to bring up the top bar, then tap the mode button in the top-right corner to switch between paged and vertical scroll reading. On wide screens, paged mode turns on the two-page spread automatically (you can turn it off in the same bar). Your choice is remembered per book.
Progress is stored on your device. With iCloud sync enabled, your library records and progress sync across your own devices through your iCloud account. Remote library passwords stay in the device Keychain and never sync.
The first time you open a book from a remote library, the whole book is cached locally so page turns stay smooth; on a slow connection or with a large file this takes a little time. After that, it opens at local speed. Books you imported locally never need this wait.
Describe your problem on the feedback page. When you come from "Settings → Report a problem" inside the app, your version and device info come along automatically, which makes diagnosis much faster.