The input buffer should be emptied after the first answer
Verify package status (anonymously) at "https://www.swi-prolog.org/pack/query" Y/n?
If you type Y+Enter here, the second answer needs no input to proceed
Install "by_unix-0.2.tgz" (15,238 bytes) Y/n? true.
As is the custom for Prolog (due to its intended use), this predicate fails if there is a problem leaving you clueless as to what went wrong. We need a general approach for this kind of problem. Like a non-backtrackable rolling log in the Prolog database.