Size belongs to the subscription — one account following one strategy — not to the strategy itself. That is what lets the same signal put one contract on an evaluation and four on a funded account.
Signal
Use the alert's own quantity, multiplied by a factor. Default factor is 1.
Fixed
The same number of contracts every time, whatever the alert says.
Risk in dollars
A fixed dollar amount per trade, divided by the stop distance. Needs
sl in the alert.Risk in percent
The same, as a percentage of the account balance.
Risk sizing can round to zero
A wide stop and a small risk budget produce less than one contract, and less than one contract is no trade. That appears in the event log as a rejection rather than as a fill you never got — check there before assuming the signal was lost.