Translation:If they had not had a visa, they would not have come to Tanzania
One of so many errors on this skill that make it frustratingly difficult to get through.
Too many errors. "They" require "visas." (Is there a plural for "Viza?") Secondly, the English is wrong. "They would not have been come" makes no sense. I could only report that my answer should have been accepted. They did not have a place to report the English sentence being wrong