@Kirime I doubt its that, mostly because counting with fingers has been done with them before and as such this time is likely related, and since mc didnt seem to have any inclinations to visit a shrine in the mountain at end of this chapter (stories often have characters understand what they are supposed to do next to further plot, simply cause author does and doesn't see alternative and more likely interpretations of events). But it
is possible you are right. In which case mc not understanding what she is meant to do shows up as a plot point later (as a form of subversion of the author tunnel-vision "trope").
My guess is that while she did barter with her "anything" and make a
deal with the god, it is likely he accepted the payment she threw into the box as the offering/payment. It might seem a bit cheap to bribe a god with material wealth, but in a world where they are real and do possess shrines I also think it makes sense that the customary offerings and ways to pray would be the legit ones. It could also be that simply the act of praying is enough, and as a medium served as a ritual to supply some form of power (which could be why it appeared and listened to prayers in the first place). This way she simply have to pray again to further her protection, or possibly just need to devote more to it such as becoming a "miko" (someone who sweeps shrine and prays often; a recurring "customer").
Mostly I think this as it is at least partly a comedy manga, so it taking a dark turn with her offering "anything" and it taking "everything" feels a bit farfetched.
Also, I really wish she had a proper sitdown with the weak girl to tell her what is up. Somewhere that has none of the spirits (such as the shrine), or at most some small ones as weak medium showed its safe to acknowledge their existence. The whole misunderstanding trope is annoying here and in the way its used. And I feel mc needs someone she could confide in.