diff --git a/poetry.lock b/poetry.lock
index 5ab3577..fbb73cc 100644
--- a/poetry.lock
+++ b/poetry.lock
@@ -1,4 +1,4 @@
-# This file is automatically @generated by Poetry 1.6.1 and should not be changed by hand.
+# This file is automatically @generated by Poetry 1.7.1 and should not be changed by hand.
 
 [[package]]
 name = "certifi"
@@ -205,6 +205,20 @@ tomli = {version = ">=1.0.0", markers = "python_version < \"3.11\""}
 [package.extras]
 testing = ["argcomplete", "attrs (>=19.2.0)", "hypothesis (>=3.56)", "mock", "nose", "pygments (>=2.7.2)", "requests", "setuptools", "xmlschema"]
 
+[[package]]
+name = "python-dotenv"
+version = "1.0.1"
+description = "Read key-value pairs from a .env file and set them as environment variables"
+optional = false
+python-versions = ">=3.8"
+files = [
+    {file = "python-dotenv-1.0.1.tar.gz", hash = "sha256:e324ee90a023d808f1959c46bcbc04446a10ced277783dc6ee09987c37ec10ca"},
+    {file = "python_dotenv-1.0.1-py3-none-any.whl", hash = "sha256:f7b63ef50f1b690dddf550d03497b66d609393b40b564ed0d674909a68ebf16a"},
+]
+
+[package.extras]
+cli = ["click (>=5.0)"]
+
 [[package]]
 name = "requests"
 version = "2.31.0"
@@ -257,4 +271,4 @@ zstd = ["zstandard (>=0.18.0)"]
 [metadata]
 lock-version = "2.0"
 python-versions = "^3.9"
-content-hash = "3f6c449228659ab834356507643a6e518be502930f969c9e2fe0d2df7a121764"
+content-hash = "a61ff63c070f59f5b799e0097acab50a5aab1f18ed6cdc38c980cd907d1fb9f1"
diff --git a/pyproject.toml b/pyproject.toml
index a4346a8..2ab109f 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -17,6 +17,10 @@ requests = "^2.28.1"
 [tool.poetry.group.test.dependencies]
 pytest = "^7.2.0"
 
+
+[tool.poetry.group.dev.dependencies]
+python-dotenv = "^1.0.1"
+
 [build-system]
 requires = ["poetry-core"]
 build-backend = "poetry.core.masonry.api"
diff --git a/src/nowpayments_api/models/payment.py b/src/nowpayments_api/models/payment.py
index 77c3999..50674c5 100644
--- a/src/nowpayments_api/models/payment.py
+++ b/src/nowpayments_api/models/payment.py
@@ -36,7 +36,7 @@ class PaymentData(Base):  # pylint: disable=too-many-instance-attributes
     payout_address: str = None
     payout_currency: str = None
     payout_extra_id: str = None
-    fixed_rate: bool = None
+    is_fixed_rate: bool = None
     is_fee_paid_by_user: bool = None
 
 
diff --git a/src/nowpayments_api/nowpayments_api.py b/src/nowpayments_api/nowpayments_api.py
index a709bfc..9117615 100644
--- a/src/nowpayments_api/nowpayments_api.py
+++ b/src/nowpayments_api/nowpayments_api.py
@@ -116,12 +116,10 @@ def create_payment(
         :param str ipn_callback_url: Url to receive callbacks, should contain "http" or "https".
         :param str order_id: Inner store order ID.
         :param str order_description: Inner store order description.
-        :param int purchase_id: id of purchase for which you want to create other payment,
-            only used for several payments for one order
         :param str payout_address: Receive funds on another address.
         :param str payout_currency: Currency of your external payout_address.
         :param int payout_extra_id: Extra id or memo or tag for external payout_address.
-        :param bool fixed_rate: Required for fixed-rate exchanges.
+        :param bool is_fixed_rate: Required for fixed-rate exchanges.
         :param bool is_fee_paid_by_user: Required for fixed-rate exchanges with all fees paid by users.
 
         :return: dict
diff --git a/tests/test_nowpayments.py b/tests/test_nowpayments.py
index 657c8f6..34e6d12 100644
--- a/tests/test_nowpayments.py
+++ b/tests/test_nowpayments.py
@@ -157,11 +157,10 @@ def test_create_payment_with_optional_paras(
         ipn_callback_url="https://example.org",
         order_id="Order_123456789",
         order_description="Roland TR-8S",
-        # purchase_id= "", # I do not understand official documentation
         # payout_address="d8dA6BF26964aF9D7eEd9e03E53415D37aA96045",  # This always returns 400
         # payout_currency="eth",  # Returns 500 probably related to the 'payout_address'
         # payout_extra_id=0xbeef, # Returns same error as payout_currency
-        fixed_rate=True,
+        is_fixed_rate=True,
         is_fee_paid_by_user=True,
     )
     assert "payment_id" in response
@@ -441,7 +440,7 @@ def test_get_list_of_payments_sort_paras_error(
         now_payments_email_password.list_of_payments(sort_by="invalid_sort_parameter")
 
 
-def test_get_list_of_payments_sort_paras_error(
+def test_get_list_of_payments_order_paras_error(
     now_payments_email_password: NOWPaymentsAPI,
 ) -> None:
     with pytest.raises(NowPaymentsException, match="Invalid order parameter"):