Over the lifecycle of an order, Tag 44 (Price) can make the difference between execution and silent failure, and you need to treat Price as structured data rather than a free-form value.
You must understand precision: some venues expect a fixed number of decimal places while others expect an integer scaled by an exponent. If you send 123.45 when the venue expects 12345 (implied by a scale of 2), your orders will either be rejected or routed at an unintended level. You should map your internal representation to the venue’s expected format and test edge cases for rounding and truncation.
You must handle scaling consistently. FIX implementations often treat Tag 44 as a floating or decimal value, but matching engines frequently store prices as signed integers with an associated tick size or multiplier. You should normalize by applying the venue tick size and lot size, and validate that the scaled value aligns to the venue grid before sending.
You should be aware of negative support. Some venues allow negative Price values for special instruments or as indicators (offsets, credit spreads, or synthetic constructions). If your client library strips signs or treats negative numbers as invalid, you will silently corrupt orders. Test negative-value paths explicitly.
You need to know about venue-specific formatting. Differences include required decimal separators, leading/trailing zero handling, scientific notation acceptance, and maximum field length. A venue that expects a plain integer but receives localized formatting (commas, thousands separators) can drop or mis-interpret Tag 44 without immediate rejection. Validate message payloads against the venue’s spec and run end-to-end simulations.
You should instrument monitoring to catch silent failures: compare sent vs. accepted price fields in confirmations, log raw FIX messages, and assert parity after any conversion. Without automated checks, mismatched precision, scaling, negative support, or venue-specific formatting will continue to break orders silently and cost you time and money.