The CA-4 agreement classifies nationalities in three categories: A, B, C.
Nicaragua and Honduras recognize Belarus citizens as "A" citizens, who are visa exempt:
.. which means that with an ordinary Belarus passport you can enter both Honduras and Nicaragua with no visa.
When you've entered the CA-4 through one of the above two countries that consider you an A citizen, can you move freely to other CA-4 countries, with a Belarus passport? No.
You can move freely between Honduras and Nicaragua, but in order to travel to Guatemala or El Salvador, you need to obtain a visa:
When one of the CA-4 countries grants a nationality an "A" category, which is otherwise considered by the CA-4 as a "B" category, and this national needs to move in the CA-4 region, to a country that requires a visa, the national will be able to apply for a Visa at the respective consulate.