His boss 'assured' him that he had her continued support. = His boss 'assured' him of her continued support. = “You have my continued support,” his boss 'assured' him.
You can 'rest assured' [=you can be sure] that these mistakes won't happen again. = 'Rest assured', these mistakes won't happen again.
They are not 'assured of' being paid. [=it is not certain that they will be paid]
(..) There's no trouble with the telephones here. I know when there is trouble and when there is not trouble. And I can definitely tell you that there is trouble. You may rest assured of that. Since when? Since it was reported. I see. What is the trouble with the telephone? (..)1975 The Return of the Pink Panther