French Foreign Legion Postmark With Letter By Captain

Seems to also say mon cher ?? femme (wife)?

A kind person just did the following translation

Mister Anselin librarian
9 street Dauphine ( Dauphine meens: the oldest daugther of the King)

Because I wanted the military journal I am joining to you a bill of the amount I owe you,
you would please me greatly if you can send it to me the sooner as possible
I would like it dated on the first of january of this year
Meanwile I am with consideration (meaning something like I will be at your disposition if you need any help or information ?)

M. Y (?) Mossod

I beg you my dear Yvan (?) to pay this amount to mister Anselin - who I have received from mister the captain Palvi,
it is to oblige this friend ... ?... ?... ? (sorry I cant read here at all)
So you will credit me, write to me if you have received the letter in question because I will write to the dépôt (déposit in English ?)

..."write to me if you have received the letter in question because I will write to the dépôt (déposit in English ?)"

The dépôt in question might actually be the Communal Depot of the Regiments (Dépôt commun des régiments) which at that time could have been located in the main city of Algiers, Algeria and probably covered the whole expeditionary force.
I believe the depot was within a year or so re-located to the coastal city of Oran, Algeria and renamed Dépôt commun des régiments étrangers.