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Overview

The Buildmarkets FIX Gateway enables two specialized order types for more flexible trading.

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Dollar Amount Orders

These orders let you specify a dollar value instead of share quantity. Key requirements: Tag 38 (OrderQty) must be 0; Tag 40 (OrdType) must be 1 (Market only); Tag 152 (CashOrderQty) contains the dollar amount. “When OrderQty=0 and CashOrderQty is set, the gateway converts the dollar amount into the appropriate share” quantity using current market pricing. A 100orderona100 order on a 228 stock would execute as approximately 0.4386 shares. Example message: 
8=FIX.4.4|35=D|49=CLIENT1|56=BROKERX|11=ORD12345|55=AAPL|54=1|38=0|40=1|60=20250430-14:22:30.000|152=100|10=123|

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Fractional Orders

These accept decimal share quantities in Tag 38 (OrderQty), such as 0.5 for half a share. Market order type (OrdType=1) is required. Example message: 
8=FIX.4.4|35=D|49=CLIENT1|56=BROKERX|11=ORD12345|55=AAPL|54=1|38=0.5|40=1|60=20250430-14:22:30.000|10=123|

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Constraints

Both order types must be Market orders only — Limit, Stop, and Stop Limit orders are not supported. The REST API offers equivalent functionality through the OrderQuantity parameter.