Answer
Check whether an alternate, more fundamental Logical Unit/table pairing for the same underlying data exposes the fields you need under slightly different names — for example, the plain Invoice Logical Unit built on the same core invoice table exposes fields like a net-currency-amount field and a rowstate field that correspond conceptually to the higher-level view's net-amount and status fields, even though they're not named identically. Building the Custom Event against that more fundamental Logical Unit/table pairing, rather than a higher-level aggregated/joined view-based LU, can expose the underlying fields you actually need even when the same-named field isn't directly available on the LU you started with.