Off campus rental reimbursement from 529 plan

I have rented an apartment for my son. The lease is under my name and my son is not listed as additional tenant (not sure why I did not add him also to the lease originally).  Can I still reimburse myself for the rental expense from the 529 plan?  If I can, does the reimbursement need to be done every month or can I do it qtly to keep it simple?  

I pay the landlord via Venmo tied to my bank account. Does that constitute as proof or should I ask the landlord to issue receipts every month?