Secondment expenses - Reimbursement

Dear All,

I will have a secondment for 1 month and my university is saying that I am not allowed to ask for any reimbursement (transport, subsistence, etc.) once back. I am wondering if this is true (knowing that I still have money in the budget) and if there is any documents clarifying what is exactly covered in a secondment (knowing that I am not paying for accomodation abroad). 

Thank you very much in advance.

Best wishes,

Zaineb