Accounting entry does depends on the terms agreed in the contract with your client like whether it is reimbursable or not.
Also depending upon the business nature of your company and frequency of such transactions it can take a suitable place in your chart of accounts. Information provided by you is not sufficient to comment upon.
It can be taken in to Business promotion expenses presuming your company is paying it for the services to be utilized by your client.
Because of this type of situations we can take signature in stamp paper which includes all type of expenses which we can take most in our favour and avoid penal action taken by IT i.e we have proof of signature on stamp paper....