Passive Voice

Hello, I have a huge doubt at this moment.

I was doing homework when I noticed something a bit confusing. The activity says I need to "Make sentences from the prompts. Use passive structures."

The thing is, I've been trying so hard to figure out the solution of these prompts given:

it / generally / believe / create / someone

The cartoon character Mickey Mouse

How do I use them? I could say "It is generally believed to have been created by someone" or "It was generally believed to have been created by someone", but both options are incorrect because it says I'm misusing the passive voice by putting these words together in this order: is/was generally believed.

Help, I need to know if there is any rule that specifies how to use "generally" in a passive voice sentence.