In dealing with legal problems of sending American money outside the country, many missionaries need their supporting churches to send money to the mission board, and then the board transfers the money to the missionary. BIMI is a mission board for independent Baptists, and problems developed when some independent Baptist churches joined the Southern Baptist Convention while they still had missionaries on the field.
For years, there was no problem, and then somebody in the Convention said something that BIMI didn't like, and BIMI demanded that their missionaries repudiate the statement or BIMI would cut them off. If anyone in the world ought to believe that a mission board has no authority to rule over missionaries, it ought to be independent Baptists.
But when someone has power, and that someone controls the money, that isn't how it works out.