Accounts receivable, AR:
Debts owed to your company, usually from sales on credit. Accounts receivable is business asset, the sum of the money owed to you by customers who haven't paid. The standard procedure in business-to-business sales is that when goods or services are delivered the come with an invoice, which is to be paid later. Business customers expect to be invoiced and to pay later. The money involved goes onto the seller's books as accounts receivable, and onto the buyer's books as accounts payable.
Business Plan Pro treats receivables with the respect they reserve, because of companies selling to businesses, they are critical to cash flow. If you set the plan for no sales on credit, then you don't see receivables, because you don't have them. Otherwise, your sales on credit assumptions appear in the General Assumptions table. The receivables balance is in the Balance Sheet, among short-term assets, where the estimate is easily adjustable.