Quick answer: Nine out of ten MT5 login failures are one of: wrong server, pasted password with a stray space, or the investor password instead of the main trading password.
Work through these in order
Select the exact Traderscale server shown in your credentials — not a similarly named one from the broker list
Type the account number and password manually rather than pasting
Remove accidental spaces before or after the password
Check similar-looking characters: O and 0, I and l and 1
Close and reopen MT5 after changing credentials
Confirm you're using the main trading password — the investor password shows the account but won't place orders
Confirm the account isn't read-only — see Why Is My Account Read Only?
Logged in but can't see or trade a symbol?
Funded accounts trade symbols with a lowercase "c" suffix — EURUSDc, GBPUSDc, XAUUSDc. The unsuffixed symbol may show in Market Watch but isn't tradable on the funded account. Open Market Watch → Show All, or search for the suffixed symbol, and confirm you're on the funded server.
Still stuck?
Send support your registered email, account number, the exact platform error, and a screenshot. Credentials are always visible in your Trader Area under Accounts Overview.
See also: Where to Find Your Login Credentials