diff --git a/homeassistant/components/transmission/__init__.py b/homeassistant/components/transmission/__init__.py
index 43a37179b03..c3c364e229b 100644
--- a/homeassistant/components/transmission/__init__.py
+++ b/homeassistant/components/transmission/__init__.py
@@ -1,7 +1,8 @@
 """Support for the Transmission BitTorrent client API."""
 from __future__ import annotations
 
-from datetime import timedelta
+from collections.abc import Callable
+from datetime import datetime, timedelta
 from functools import partial
 import logging
 import re
@@ -27,7 +28,11 @@ from homeassistant.const import (
     Platform,
 )
 from homeassistant.core import HomeAssistant, ServiceCall, callback
-from homeassistant.exceptions import ConfigEntryAuthFailed, ConfigEntryNotReady
+from homeassistant.exceptions import (
+    ConfigEntryAuthFailed,
+    ConfigEntryNotReady,
+    HomeAssistantError,
+)
 from homeassistant.helpers import (
     config_validation as cv,
     entity_registry as er,
@@ -159,7 +164,9 @@ async def async_unload_entry(hass: HomeAssistant, config_entry: ConfigEntry) ->
     return unload_ok
 
 
-async def get_api(hass, entry):
+async def get_api(
+    hass: HomeAssistant, entry: dict[str, Any]
+) -> transmission_rpc.Client:
     """Get Transmission client."""
     host = entry[CONF_HOST]
     port = entry[CONF_PORT]
@@ -205,24 +212,26 @@ def _get_client(hass: HomeAssistant, data: dict[str, Any]) -> TransmissionClient
 class TransmissionClient:
     """Transmission Client Object."""
 
-    def __init__(self, hass, config_entry):
+    def __init__(self, hass: HomeAssistant, config_entry: ConfigEntry) -> None:
         """Initialize the Transmission RPC API."""
         self.hass = hass
         self.config_entry = config_entry
         self.tm_api: transmission_rpc.Client = None
-        self._tm_data: TransmissionData = None
-        self.unsub_timer = None
+        self._tm_data: TransmissionData | None = None
+        self.unsub_timer: Callable[[], None] | None = None
 
     @property
     def api(self) -> TransmissionData:
         """Return the TransmissionData object."""
+        if self._tm_data is None:
+            raise HomeAssistantError("data not initialized")
         return self._tm_data
 
     async def async_setup(self) -> None:
         """Set up the Transmission client."""
 
         try:
-            self.tm_api = await get_api(self.hass, self.config_entry.data)
+            self.tm_api = await get_api(self.hass, dict(self.config_entry.data))
         except CannotConnect as error:
             raise ConfigEntryNotReady from error
         except (AuthenticationError, UnknownError) as error:
@@ -328,12 +337,12 @@ class TransmissionClient:
                 self.config_entry, options=options
             )
 
-    def set_scan_interval(self, scan_interval):
+    def set_scan_interval(self, scan_interval: float) -> None:
         """Update scan interval."""
 
-        def refresh(event_time):
+        def refresh(event_time: datetime):
             """Get the latest data from Transmission."""
-            self._tm_data.update()
+            self.api.update()
 
         if self.unsub_timer is not None:
             self.unsub_timer()
diff --git a/homeassistant/components/transmission/config_flow.py b/homeassistant/components/transmission/config_flow.py
index b7784fbe4a9..d1005f5e84c 100644
--- a/homeassistant/components/transmission/config_flow.py
+++ b/homeassistant/components/transmission/config_flow.py
@@ -57,7 +57,9 @@ class TransmissionFlowHandler(config_entries.ConfigFlow, domain=DOMAIN):
         """Get the options flow for this handler."""
         return TransmissionOptionsFlowHandler(config_entry)
 
-    async def async_step_user(self, user_input=None):
+    async def async_step_user(
+        self, user_input: dict[str, Any] | None = None
+    ) -> FlowResult:
         """Handle a flow initialized by the user."""
         errors = {}
 
@@ -141,7 +143,9 @@ class TransmissionOptionsFlowHandler(config_entries.OptionsFlow):
         """Initialize Transmission options flow."""
         self.config_entry = config_entry
 
-    async def async_step_init(self, user_input=None):
+    async def async_step_init(
+        self, user_input: dict[str, Any] | None = None
+    ) -> FlowResult:
         """Manage the Transmission options."""
         if user_input is not None:
             return self.async_create_entry(title="", data=user_input)