Full Idea
Frege's account suffered from a lack of precision about when two sets of truth-conditions should count as equivalent. (Wittgenstein aimed to rectify this defect).
Gist of Idea
Frege failed to show when two sets of truth-conditions are equivalent
Source
report of Gottlob Frege (On Sense and Reference [1892]) by Michael Potter - The Rise of Analytic Philosophy 1879-1930 50 Intro
Book Reference
Potter,Michael: 'The Rise of Anaytic Philosophy 1879-1930' [Routledge 2020], p.335