TypeScript Cannot find module despite it being installed

TypeScript reports Cannot find module for an installed npm package. Works at runtime but type checking fails.

Causes: (1) No types -- install @types/package-name. (2) Wrong moduleResolution -- use bundler or node16. (3) Package uses exports field but TS version is old (need 4.7+). (4) Path alias misconfigured.

TypeScript type resolution is separate from Node module resolution. A package can be importable but invisible to the type checker.