They don't. They're not STP if they fix spreads

How does fixed spread work for STP broker?

The fx market doesn't operate in fixed spreads. Banks don't trade fx with each other at fixed spreads because the spread is a function of the bid/offer, the market depth at the bid/offer and these are variable. There's plenty of fixed spread brokers ...

Is there a Broker Fixed spread , No slippage

No such thing as a guaranteed stop loss my man, unless that is the broker is a market makers. FX doesn't have guaranteed stops, you're filled at the next available price - which will depend on market conditions and the level & quality of liquidity ...

Broker whichs supports MT4, with low spread and little slippage.

Is it just manual trading allowed or can you use an EA?

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