This is conjectural, but building on Nick Decroos's answer and cnread's comments, appactim may be intended as an adverb meaning something like "(fixed) fast".
Formally, it's pretty clearly an adverb in -im (as in verbatim etc.), and the stem does seem to be that of pangō "fix, fasten" with the prefix ad-. I'm not finding any attestations for a verb appangō; ...
I could not find appactim in either, in dictionaries or online.
Latindict gave for the stem 'appact' a page.
The associated verb means 'fasten to'.
However, I don't know why there is the suffic '-im' (assuming that appactim is derived from 'appangere').
As stated by cnread in the comments of this answer, -im could be an adverbial suffix.