The barter sales are a service/product for a service/product. You record the purchase from your vendor (expense) and record your service as the payment of the expense. The puchase of services will equal your payment of services. For barter transactions the income equals the expense.
Since you have not used your vendor's services, you have a credit with the vendor now but the expense is recorded with the income whether you use the service now or later. Correspondingly you have a credit from the vendor.
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