Eddy, you might find the braking circuit was cutting in with the chattering, and adding to the problem.

You really need to measure voltages.
The transformer should produce 230V, and the contactor needs 230V.

We already know the contactor isn't getting 230V, so you need to measure things, and see where the voltage is dropping.
Start at the transformer. Does the output voltage drop significantly when trying to start the machine?
If it does, then measure the input voltage.
If it doesn't drop, then you need to work your way through the various things that can control the 230V on it's route from the transformer to the contactor.