program: relax fee tier constraints for maker tier (#1876)

* program: fix-fee-validate-different-denoms

* fix build

* CHANGELOG

---------

Co-authored-by: Chris Heaney <[email protected]>

Author: 0xbigz

CHANGELOG.md

@@ -15,6 +15,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixes
 
+- program: relax fee tier constraints for maker ([#1876](https://github.com/drift-labs/protocol-v2/pull/1876))
+
 ### Breaking
 
 ## [2.136.0] - 2025-09-03

programs/drift/src/validation/fee_structure.rs

@@ -3,6 +3,7 @@ use crate::msg;
 use crate::error::{DriftResult, ErrorCode};
 use crate::math::constants::{
     FEE_DENOMINATOR, FEE_PERCENTAGE_DENOMINATOR, OPEN_ORDER_MARGIN_REQUIREMENT,
+    PERCENTAGE_PRECISION,
 };
 use crate::state::state::{FeeStructure, FeeTier};
 use crate::validate;
@@ -89,14 +90,26 @@ pub fn validate_fee_tier(
     )?;
 
     let taker_fee = fee_tier.fee_numerator * (100 - fee_tier.referee_fee_numerator) / 100;
-    let fee_to_market = taker_fee
-        - fee_tier.maker_rebate_numerator
+    let fee_to_market_pre_maker = taker_fee
         - taker_fee * (fee_tier.referrer_reward_numerator + filler_reward_numerator) / 100;
 
     validate!(
-        fee_to_market <= fee_tier.fee_numerator,
+        fee_to_market_pre_maker <= fee_tier.fee_numerator,
         ErrorCode::InvalidFeeStructure,
-        "invalid fee to market ({}) for index ({})",
+        "invalid taker fee to market ({}) for index ({})",
+        fee_tier.referrer_reward_numerator,
+        fee_tier_index,
+    )?;
+
+    let fee_to_market = fee_to_market_pre_maker as u128 * PERCENTAGE_PRECISION
+        / fee_tier.fee_denominator as u128
+        - fee_tier.maker_rebate_numerator as u128 * PERCENTAGE_PRECISION
+            / fee_tier.maker_rebate_denominator as u128;
+
+    validate!(
+        fee_to_market >= 0,
+        ErrorCode::InvalidFeeStructure,
+        "invalid maker fee to market ({}) for index ({})",
         fee_tier.referrer_reward_numerator,
         fee_tier_index,
     )?;