diff --git a/src/murfey/client/multigrid_control.py b/src/murfey/client/multigrid_control.py
index a52bb0430..ab1bade3d 100644
--- a/src/murfey/client/multigrid_control.py
+++ b/src/murfey/client/multigrid_control.py
@@ -403,7 +403,8 @@ def _start_dc(self, json, from_form: bool = False):
         # it is then necessary to extract the data from the message
         if from_form:
             json = json.get("form", {})
-            json = {k: str(v) for k, v in json.items()}
+            # Safely convert all entries into strings, but leave None as-is
+            json = {k: str(v) if v is not None else None for k, v in json.items()}
         self._environment.data_collection_parameters = {
             k: None if v == "None" else v for k, v in json.items()
         }
@@ -411,7 +412,7 @@ def _start_dc(self, json, from_form: bool = False):
         context = self.analysers[source]._context
         if isinstance(context, TomographyContext):
             if from_form:
-                requests.post(
+                capture_post(
                     f"{self._environment.url.geturl()}/clients/{self._environment.client_id}/tomography_processing_parameters",
                     json=json,
                 )
@@ -442,7 +443,7 @@ def _start_dc(self, json, from_form: bool = False):
                 )
                 eer_fractionation_file = eer_response.json()["eer_fractionation_file"]
                 json.update({"eer_fractionation_file": eer_fractionation_file})
-            requests.post(
+            capture_post(
                 f"{self._environment.url.geturl()}/sessions/{self._environment.murfey_session}/tomography_preprocessing_parameters",
                 json=json,
             )
diff --git a/src/murfey/instrument_server/api.py b/src/murfey/instrument_server/api.py
index cb67ea25f..445faa59b 100644
--- a/src/murfey/instrument_server/api.py
+++ b/src/murfey/instrument_server/api.py
@@ -351,7 +351,11 @@ def upload_gain_reference(
         )
 
     # Return the rsync URL if set, otherwise assume you are syncing via Murfey
-    rsync_url = urlparse(str(machine_config.get("rsync_url", _get_murfey_url())))
+    rsync_url = urlparse(
+        str(machine_config["rsync_url"])
+        if machine_config.get("rsync_url", "")
+        else _get_murfey_url()
+    )
     rsync_module = machine_config.get("rsync_module", "data")
     rsync_path = f"{rsync_url.hostname}::{rsync_module}/{safe_visit_path}/{safe_destination_dir}/{secure_filename(gain_reference.gain_path.name)}"
 
diff --git a/src/murfey/util/models.py b/src/murfey/util/models.py
index d72eff927..b9a5e60b3 100644
--- a/src/murfey/util/models.py
+++ b/src/murfey/util/models.py
@@ -368,7 +368,7 @@ class PreprocessingParametersTomo(BaseModel):
     eer_fractionation: int
 
     class Base(BaseModel):
-        dose_per_frame: float
+        dose_per_frame: Optional[float]
         gain_ref: Optional[str]
         manual_tilt_offset: float
         eer_fractionation: int
diff --git a/tests/conftest.py b/tests/conftest.py
index 6672188ba..9176d86a1 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -1,4 +1,5 @@
 import json
+from configparser import ConfigParser
 
 import pytest
 from sqlmodel import Session
@@ -21,6 +22,20 @@ def start_postgres():
         murfey_db.commit()
 
 
+@pytest.fixture()
+def mock_client_configuration() -> ConfigParser:
+    """
+    Returns the client-side configuration file as a pre-loaded ConfigParser object.
+    """
+    config = ConfigParser()
+    config["Murfey"] = {
+        "instrument_name": "murfey",
+        "server": "http://0.0.0.0:8000",
+        "token": "pneumonoultramicroscopicsilicovolcanoconiosis",
+    }
+    return config
+
+
 @pytest.fixture()
 def mock_security_configuration(tmp_path):
     config_file = tmp_path / mock_security_config_name
diff --git a/tests/instrument_server/test_api.py b/tests/instrument_server/test_api.py
new file mode 100644
index 000000000..b4fa9cd73
--- /dev/null
+++ b/tests/instrument_server/test_api.py
@@ -0,0 +1,147 @@
+from pathlib import Path
+from typing import Optional
+from unittest.mock import ANY, Mock, patch
+from urllib.parse import urlparse
+
+from pytest import mark
+
+from murfey.instrument_server.api import (
+    GainReference,
+    _get_murfey_url,
+    upload_gain_reference,
+)
+from murfey.util import posix_path
+
+test_get_murfey_url_params_matrix = (
+    # Server URL to use
+    ("default",),
+    ("0.0.0.0:8000",),
+    ("murfey_server",),
+    ("http://murfey_server:8000",),
+    ("http://murfey_server:8080/api",),
+)
+
+
+@mark.parametrize("test_params", test_get_murfey_url_params_matrix)
+def test_get_murfey_url(
+    test_params: tuple[str],
+    mock_client_configuration,  # From conftest.py
+):
+    # Unpack test_params
+    (server_url_to_test,) = test_params
+
+    # Replace the server URL from the fixture with other ones for testing
+    if server_url_to_test != "default":
+        mock_client_configuration["Murfey"]["server"] = server_url_to_test
+
+    # Mock the module-wide config variable with the fixture value
+    # The fixture is only loaded within the test function, so this patch
+    # has to happen inside the function instead of as a decorator
+    with patch("murfey.instrument_server.api.config", mock_client_configuration):
+        known_server = _get_murfey_url()
+
+    # Prepend 'http://' to config URLs that don't have it for the comparison
+    # Otherwise, urlparse stores it under the 'path' attribute
+    original_url = str(mock_client_configuration["Murfey"].get("server"))
+    if not original_url.startswith(("http://", "https://")):
+        original_url = f"http://{original_url}"
+
+    # Check that the components of the result match those in the config
+    parsed_original = urlparse(original_url)
+    parsed_server = urlparse(known_server)
+    assert parsed_server.scheme in ("http", "https")
+    assert parsed_server.hostname == parsed_original.hostname
+    assert parsed_server.port == parsed_original.port
+    assert parsed_server.netloc == parsed_original.netloc
+    assert parsed_server.path == parsed_original.path
+
+
+test_upload_gain_reference_params_matrix = (
+    # Rsync URL settings
+    ("http://1.1.1.1",),  # When rsync_url is provided
+    ("",),  # When rsync_url is blank
+    (None,),  # When rsync_url not provided
+)
+
+
+@mark.parametrize("test_params", test_upload_gain_reference_params_matrix)
+@patch("murfey.instrument_server.api.subprocess")
+@patch("murfey.instrument_server.api.tokens")
+@patch("murfey.instrument_server.api._get_murfey_url")
+@patch("murfey.instrument_server.api.requests")
+def test_upload_gain_reference(
+    mock_request,
+    mock_get_server_url,
+    mock_tokens,
+    mock_subprocess,
+    test_params: tuple[Optional[str]],
+):
+
+    # Unpack test parameters and define other ones
+    (rsync_url_setting,) = test_params
+    server_url = "http://0.0.0.0:8000"
+    instrument_name = "murfey"
+    session_id = 1
+
+    # Create a mock machine config base on the test params
+    rsync_module = "data"
+    gain_ref_dir = "C:/ProgramData/Gatan/Gain Reference"
+    mock_machine_config = {
+        "rsync_module": rsync_module,
+        "gain_reference_directory": gain_ref_dir,
+    }
+    if rsync_url_setting is not None:
+        mock_machine_config["rsync_url"] = rsync_url_setting
+
+    # Assign expected values to the mock objects
+    mock_response = Mock()
+    mock_response.status_code = 200
+    mock_response.json.return_value = mock_machine_config
+    mock_request.get.return_value = mock_response
+    mock_get_server_url.return_value = server_url
+    mock_subprocess.run.return_value = Mock(returncode=0)
+
+    # Construct payload and pass request to function
+    gain_ref_file = f"{gain_ref_dir}/gain.mrc"
+    visit_path = "2025/aa00000-0"
+    gain_dest_dir = "processing"
+    payload = {
+        "gain_path": gain_ref_file,
+        "visit_path": visit_path,
+        "gain_destination_dir": gain_dest_dir,
+    }
+    result = upload_gain_reference(
+        instrument_name=instrument_name,
+        session_id=session_id,
+        gain_reference=GainReference(
+            **payload,
+        ),
+    )
+
+    # Check that the machine config request was called
+    machine_config_url = f"{server_url}/instruments/{instrument_name}/machine"
+    mock_request.get.assert_called_once_with(
+        machine_config_url,
+        headers={"Authorization": ANY},
+    )
+
+    # Check that the subprocess was run with the expected arguments
+    # If no rsync_url key is provided, or rsync_url key is empty,
+    # It should default to the server URL
+    expected_rsync_url = (
+        urlparse(server_url) if not rsync_url_setting else urlparse(rsync_url_setting)
+    )
+    expected_rsync_path = f"{expected_rsync_url.hostname}::{rsync_module}/{visit_path}/{gain_dest_dir}/gain.mrc"
+    expected_rsync_cmd = [
+        "rsync",
+        posix_path(Path(gain_ref_file)),
+        expected_rsync_path,
+    ]
+    mock_subprocess.run.assert_called_once_with(
+        expected_rsync_cmd,
+        capture_output=True,
+        text=True,
+    )
+
+    # Check that the function ran through to completion successfully
+    assert result == {"success": True}