I run pg_repack --help and I get this:
-C, --exclude-extension don't repack tables which belong to specific extension
--error-on-invalid-index don't repack tables which belong to specific extension
Maybe the --error-on-invalid-index line was copied from --exclude-extension line but the author forgot to edit it after coping.
printf(" -C, --exclude-extension don't repack tables which belong to specific extension\n");
printf(" --error-on-invalid-index don't repack tables which belong to specific extension\n");