Facebook permissions are a pain-in-the-ass sometimes. If someone posts something that only friends or friends-of-friends can view, then sharing it gives anyone else the "attachment unavailable" message.
Whatever the attachment is in your post, in the format it is currently in, the majority of the people in this group can't see it. What is it that you are trying to share?
Sure, I could send you a friend request and solve the issue for myself, but that still leaves the majority of the group unable to read this. Let's solve this problem for good.
Okay, go back to your original post on your timeline. At the top, there should be a small drop-down menu that allows you to edit the privacy settings. Set it to "Public", and everyone will be able to see.
I would send a Notice of Claim, before the invoice...
Notifying them my intent to CLAIM, and WHY I will claim.
That way, they will have the opportunity to tell me WHY I shouldn't claim if they want....
And then, after 3 or whatever the amount of days I decide, I will send an invoice, unless they've explained to me on WHY I shouldn't claim :)
But that's just me :D