Right, that's the exact model you should look for, InReach is the term they use to describe their whole sat-messaging line.
By the way, they also have an API you can hook into.
I once was toying with the idea of implementing a compact language to help me with resupplying between towns:
Lets say that my flashlight breaks or my mattress gets a hole that I cannot fix, I could have a list of all my items (it's rather short - for example here is my '19 HRP thruhike gear list: https://lighterpack.com/r/rbjo9d).
For every item I can maintain let's say an amazon product page (with some price bound probably), as well as the list of towns I'll be visiting.
A single text message that says "ORDER 1 flashlight to Bridgeport" could trigger an order to the General Delivery address which I already have in my Amazon account.
This could even work as a service that possibly pays itself using just Amazon's referral fees.
I never got to actually testing their API since you have to manually apply to their business plan which cost significantly more than the regular plan.
But it could really be useful and save you a lot of time and money while thruhiking, when you really need to get a replacement item while out there between towns with no signal and your next town only has a general store.
And yes, Otter's story is so crazy, sad and depressing. Being there so long and slowly realizing that there is no way out feels so difficult to process.
I can easily see how it could have been adapted to a film.