The "Invalid Account" error occurs when MetaTrader cannot authenticate your login credentials. There may be 3 reasons why this could happen:
Incorrect login
You can find your account number in the Client Portal. Click Trading > My Accounts.
Incorrect password
Ensure you use the correct Trading Password when you log in. If you have forgotten your password, you can change it in your Client Terminal under My Account. It can be reset by clicking on the three dots "•••" beside your account.
Incorrect server
You may be connected to the wrong server. Check which server your account uses in your Client Portal under My Account. Please check the trading server under the trading account number and ensure you log in using the correct server.