We sent a letter that my husband wrote explaining that he supports the home, and that I dedicate myself to study at the same time. He also explained that I have a prepaid card linked to his bank account where he provides me with money for my personal expenses.
As proof of cohabitation we send correspondence in the name of both, with similar dates, a copy of the lease agreement where they clarify that we are a family and although I have no responsibility to pay the rent, he cannot make changes to the contract without my knowledge. You can ask your landlord to write a letter explaining that you live together.
My husband's grandfather wrote another letter explaining that we live with the 6 months and testify that we have a marital relationship.
We sent a fragment of my husband's employment letters and a letter from my school where they say that I attend that school to French classes because of its proximity to my home.
And a copy of my husband's insurance policy where I am a beneficiary.
It took just 15 days to pass these proofs when we sent them out.