Why: You wired a '{pinA}' output to a '{pinB}' input — UE5 doesn't know how to convert between them. The compiler refuses to insert an implicit cast for unsafe conversions.

Fix: Right-click between the two nodes and look for a conversion node (e.g. ToString, Truncate, Cast To). If converting between Object types, use Cast To. For numeric conversions, use the dedicated converter nodes. If the conversion truly doesn't make sense, the wiring is logically wrong — re-check the design.