What's more correct?

many lies
or many lie

that is for "Too many lies/lie"

You always have to use plural forms after many, You can't use a singular after ''many''. So, ''many lie'' is incorrect.

Most of the time it'd be "too many lies"....example:

"There were too many lies in his story."

However, there could also be a dialogue like this:

PERSON A: "Why don't you believe any of those people?"
PERSON B: "Too many of them lie." OR "Too many people lie." (this is because of 'people')

PERSON A: "Some of those people tell the truth."
PERSON B: "Yes, some do but many lie."
PERSON A: "What makes you think so?"
PERSON B: "I've heard many lies from them."
PERSON A: "How many?"
PERSON B: "Too many."

"Many lie." can mean "Many people lie."

Mes chers petits lapins,

In "many people lie" or "many lie", "lie" is used as a verb.
In "I've heard many lies", "lies" is used as a noun.

Hope that's helpful.

Tippie,

your explanation was certainely helpful to some learners.
However, to refer the other contributors of this thread as your "dear little rabbits" was not.