fix(utxo): calculate min_trading_vol based on fixed tx fees

mm2src/coins/utxo/utxo_common.rs

@@ -3416,8 +3416,24 @@ pub fn min_tx_amount(coin: &UtxoCoinFields) -> BigDecimal {
 }
 
 pub fn min_trading_vol(coin: &UtxoCoinFields) -> MmNumber {
-    let dust_multiplier = MmNumber::from(10);
-    dust_multiplier * min_tx_amount(coin).into()
+    let min_from_dust = coin.dust_amount * 10;
+
+    let fixed_fee_rate = match coin.tx_fee {
+        FeeRate::FixedPerKb(sats) => Some(ActualFeeRate::FixedPerKb(sats)),
+        FeeRate::FixedPerKbDingo(sats) => Some(ActualFeeRate::FixedPerKbDingo(sats)),
+        // The output of this function must be deterministic for the lifetime of
+        // an order / swap, we will use the dust-based calculation.
+        FeeRate::Dynamic(_) => None,
+    };
+
+    let min_from_fee = fixed_fee_rate.map_or(min_from_dust, |fee_rate| {
+        fee_rate.get_tx_fee(DEFAULT_SWAP_TX_SPEND_SIZE) * 10
+    });
+
+    // The final minimum volume must be large enough to satisfy both the dust and the fee constraints.
+    let min_vol_sats = std::cmp::max(min_from_dust, min_from_fee);
+
+    big_decimal_from_sat_unsigned(min_vol_sats, coin.decimals).into()
 }
 
 pub fn is_asset_chain(coin: &UtxoCoinFields) -> bool {