Shogun 2 Trade Agreement Unacceptable
I think I know why that is happening. Other clans will terminate contracts with you (including trade agreements) if your diplomatic reputation with them falls below a certain threshold (which you have not seen). This would explain why they now want a payment to restore trade with you. As others have said, it can also be a precursor to a declaration of war against you. Shogun`s AI 2 is very expansionist and will declare war on friendly clans to conquer the territory. That`s one of the reasons I like Shogun 2, the AI is programmed (in a way) to do what a human player would do, which is to declare war on a clan of friends if they don`t have other means of expansion. In the countryside, the actor must see the development of the colonies, military production, economic growth and technological progress. Armies and units are organized by the player and move around the stylized campaign map to fight battles with other factions. In addition to combat, the player is capable of diplomacy, political maneuvering and the use of special agents to gain the upper hand. Ninja and Geisha are also assassins and spies.  Although religion is not as relevant as in Medieval II: Total War, it cannot be overlooked by the player. Greater interaction with European foreigners (Nanban merchants), for example to promote trade and buy firearms, exposes the clan to Christianity, which will seriously exacerbate religious unrest in the provinces. Religious agents, such as monks and priests, can be used to convert enemy populations.
The Portuguese arrived in Japan in 1543. Nagasaki became an important trading port with the Portuguese, which led Japan to open trade relations and contacts between the rest of the world, especially with mainland China, with which Japan had severed trade relations following a series of incidents. The Portuguese, who now acted as intermediaries between the two Asian countries, both merchants and kyushu daimyo (feudal lords) expected to reap great benefits from these trades with the Portuguese. This introduced Christianity, firearms and gunpowder to Japan. Shogun 2 played in feudal Japan in the 16th century, after the war during the Ashikaga Shogunate. The country is fragmented into rival clans, led by local warlords who each fight for control. The player takes the direction of one of these clans, with the aim of dominating other factions and establishing domination over Japan. The standard edition of the game has a total of eight groups (plus a ninth faction for the tutorial), each with a unique starting position and different political and military forces.
The limited edition contains an exclusive ninja clan, the Hattori, and a DLC releases a tenth clan, the Ikko-Ikki.   As I said before, commercial nodes are on a first come first serve basis, so if you don`t want to wage war on your ally, you have to wait for them to decide to leave the port.