FORCDK-TREE-001
Thrown by forty-cdk/tree.
[forty-cdk/tree] FORCDK-TREE-001: {piece} must be used inside a [forTree] element.Cause
No FOR_TREE_CONTEXT provider is visible from {piece}. Angular resolves a directive's dependencies at the template's declaration site rather than where it is stamped, so a piece declared in an ng-template outside the root resolves nothing even when it renders inside it.
Fix
Move {piece} inside a [forTree] element, declaring any ng-template it lives in there too.
Where it comes from
projects/forty-cdk/tree/src/tree-context.ts:291
A value in braces is filled in when the message is reported, so the sentence in your console names the piece, input or value that failed.