We pay advertising expenses that are 50% recoverable from the customer. First, we invoice the customer for their 50% share of the expenses, and then we pay the full amount (including both the customer's and our shares) to the advertising agency.

Would it be correct if record expenses as expenses receivable.

Mark them billable to the client

When 50% received as a cash/bank

Cash/bank Dr

Expenses receivable cr

Pay our 100% 

Expenses Dr

Bank/cash cr.