Sources for Exchange variance adjustment Rule in Event Type Invoice Price for Receipt Accounting

Summary:

Sources for Exchange variance adjustment Rule in Event Type Invoice Price for Receipt Accounting
In Receipt Accounting Accounting class Exchange variance adjustments in Event Type Invoice Price Adjustment is failing with error
The input source values don't map to any output value defined in mapping set Exchange Variance Adjustment.
We are using standard Account Rule "Exchange Variance Adjustment" and expected to Pick the Priority 1
Source Code Combination Identifier with condition

"Accounting Line Type"(CMR,S,S) = EXCHANGE_VARIANCE_ADJUSTMENT 'And' "Code Combination Identifier"."All"(CMR,S,S) Is not null
But instead system is picking Priority 2. Though we have PO charge charge Account available in transaction.