// First, approve the funds to the helper if needed
    if (!LibAsset.isEther(txData.receivingAssetId) && toSend > 0) {
      require(LibERC20.approve(txData.receivingAssetId, txData.callTo, toSend), "fulfill: APPROVAL_FAILED");
    }

    // Next, call `addFunds` on the helper. Helpers should internally
    // track funds to make sure no one user is able to take all funds
    // for tx
    if (toSend > 0) {
      try
        IFulfillHelper(txData.callTo).addFunds{ value: LibAsset.isEther(txData.receivingAssetId) ? toSend : 0}(
          txData.user,
          txData.transactionId,
          txData.receivingAssetId,
          toSend
        )
      {} catch {
        // Regardless of error within the callData execution, send funds
        // to the predetermined fallback address
        require(
          LibAsset.transferAsset(txData.receivingAssetId, payable(txData.receivingAddress), toSend),
          "fulfill: TRANSFER_FAILED"
        );
      }
    }
