How to get BudgetTransactionPayload hash?

I'm working with the REST APIs for Budgetary Control (specifically the Budgetary Control for Enterprise Performance Management Budget Transactions) and am trying to retrieve the BudgetTransactionPayload, which is a hash key of the attributes that make up the composite key of the transaction. The server parses this payload in order to retrieve the budget period, year, and other essential information for the transaction. It says to use the following in order to do this:

/fscmRestApi/resources/11.13.18.05/budgetaryControlBudgetTransactions/{budgetaryControlBudgetTransactionsUniqID}/enclosure/BudgetTransactionPayload

I've been testing using another endpoint which is the following:

/fscmRestApi/resources/11.13.18.05/budgetaryControlBudgetTransactions

This endpoint is for creating and performing validation on a budget entry. I played around with it a little to see what sorts of responses I get if I didn't include the payload, and it fails (of course) but also gives me a series of links, one of which matches the one for retrieving the BudgetTransactionPayload with what ostensibly is the unique ID provided.