I can't guarantee that this is the problem because you did not really describe where the leak is, but a common place for a leak is where the supply line connects to the toilet, usually in the back. The manufacturers' instructions are to tighten the fittings "finger tight." If the leak is there, tighten it a little bit more, using pliers if necessary, but DO NOT over do it. Usually the toilet is held in place with a couple of nuts/bolts. You may have to tip the toilet forward to gain access to the supply line.
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