Hello, I don't think that's a bug, if you read the manpage, it indicates that it accepts v4 or v6 only, depending on how weborf was compiled.
On debian it is compiled for ipv6, so basically it only uses ipv6 (and works with ipv4 with mapped addresses). Maybe it should be written more clearly? Both in the manpage and in the error that gets printed? I do not plan to change it to accept ipv4 addresses. Best
