Game concept
Diplomacy Contract
The game also links it as Diplomacy Contracts, Diplomacy Contract's, Diplomacy Contracts'.
From the game's encyclopedia
A Diplomacy Contract typically involves settling local disputes or negotiating advantageous deals using your wit.
The game's text for patch 1.20.1.2. Words in blue are entries of the encyclopedia: hover one to read it, as in the game.
Diplomacy Contract is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "A Diplomacy Contract typically involves settling local disputes or negotiating advantageous deals using your wit." It is part of task_contracts. The game also links it as Diplomacy Contracts, Diplomacy Contract's and Diplomacy Contracts'. Patch 1.20.1.2, from game/common/game_concepts/07_ep3_game_concepts.txt and game/localization/english/game_concepts_l_english.yml.
Source: game/common/game_concepts/07_ep3_game_concepts.txt, game/localization/english/game_concepts_l_english.yml and the English localisation, Crusader Kings III 1.20.1.2.