I believe that,as long as paid there must have been harveste

语法不对,句子的意思是：“我相信,只要付出就一定会有收获”
“there must have been”是“there be”句型,意思是：“有”,must是情态动词“一定”,must have been 是对过去情况的推测.
所以“be”后面不是被动态,而是要加名词,收获的名词“harvest”
正确的应该是“I believe that,as long as paid,there must have been harvest.”