diff --git a/src/access_py_telemetry/api.py b/src/access_py_telemetry/api.py
index 360cdcd..c222a66 100644
--- a/src/access_py_telemetry/api.py
+++ b/src/access_py_telemetry/api.py
@@ -11,6 +11,7 @@
 import httpx
 import asyncio
 import pydantic
+import re
 import yaml
 import multiprocessing
 from pathlib import Path, PurePosixPath
@@ -171,9 +172,7 @@ def send_api_request(
                 f"Endpoint for '{service_name}' not found in {self.endpoints}"
             ) from e
 
-        endpoint = str(PurePosixPath(self.server_url) / endpoint.lstrip("/")).replace(
-            "http:/", "http://"
-        )
+        endpoint = _format_endpoint(self.server_url, endpoint)
 
         send_in_loop(endpoint, telemetry_data, self._request_timeout)
         return None
@@ -377,3 +376,12 @@ def _run_in_proc(endpoint: str, telemetry_data: dict[str, Any], timeout: float)
             stacklevel=2,
         )
     return None
+
+
+def _format_endpoint(server_url: str, endpoint: str) -> str:
+    """
+    Concatenates the server URL and endpoint, ensuring that there is only one
+    slash between them.
+    """
+    endpoint = str(PurePosixPath(server_url) / endpoint.lstrip("/"))
+    return re.sub(r"^(https?:/)", r"\1/", endpoint)
diff --git a/tests/test_api.py b/tests/test_api.py
index 47bd0cb..7b8728f 100644
--- a/tests/test_api.py
+++ b/tests/test_api.py
@@ -4,7 +4,12 @@
 """Tests for `access_py_telemetry` package."""
 
 import access_py_telemetry.api
-from access_py_telemetry.api import SessionID, ApiHandler, send_in_loop
+from access_py_telemetry.api import (
+    SessionID,
+    ApiHandler,
+    send_in_loop,
+    _format_endpoint,
+)
 from pydantic import ValidationError
 import pytest
 
@@ -281,3 +286,32 @@ def test_api_handler_set_timeout(api_handler):
     api_handler.request_timeout = None
 
     assert api_handler.request_timeout is None
+
+
+@pytest.mark.parametrize(
+    "server_url, endpoint, expected",
+    [
+        (
+            "http://localhost:8000",
+            "/some/endpoint",
+            "http://localhost:8000/some/endpoint",
+        ),
+        (
+            "http://localhost:8000/",
+            "some/endpoint/",
+            "http://localhost:8000/some/endpoint",
+        ),
+        (
+            "https://localhost:8000",
+            "/some/endpoint",
+            "https://localhost:8000/some/endpoint",
+        ),
+        (
+            "https://localhost:8000/",
+            "some/endpoint/",
+            "https://localhost:8000/some/endpoint",
+        ),
+    ],
+)
+def test_format_endpoint(server_url, endpoint, expected):
+    assert _format_endpoint(server_url, endpoint) == expected