What it means
'Not enough money' means the trade you are trying to open needs more margin than your account has available. Margin is the deposit the broker holds while a leveraged position is open. If your free margin is below what the order requires, the platform refuses it.
It is not saying your balance is zero — it is saying this particular position is too big for what is free right now.
Common causes
The lot size is too large for your balance. You already have open trades using up margin, leaving little free. Your account leverage is lower than you assumed, so each lot ties up more money. Or the symbol has a high margin requirement (some indices, metals, and crypto CFDs need far more per lot than major currency pairs).
Step-by-step fix
Look at the Trade tab: check 'Free Margin'. Then reduce your lot size and try again — halving the volume roughly halves the margin needed.
Close or reduce other open positions to free up margin. Confirm your account leverage in the account details or with support. If you genuinely need a bigger position, you may need to deposit more, but never deposit money you cannot afford to lose just to force a trade through.
How to prevent it
Size positions from your balance and risk per trade, not from what the platform will let you get away with. Learn the margin requirement of each symbol before trading it. Keep a buffer of free margin so normal price moves do not push you into trouble.
Broker's fault or yours?
This is on your side — it is a sizing and margin issue, not a broker fault. It is actually the platform protecting you from over-leveraging. Treat it as a useful warning that the trade is too large.