diff --git a/src/controllers/api/guildTechController.ts b/src/controllers/api/guildTechController.ts
index 34022699..b9d3b75d 100644
--- a/src/controllers/api/guildTechController.ts
+++ b/src/controllers/api/guildTechController.ts
@@ -54,10 +54,8 @@ export const guildTechController: RequestHandler = async (req, res) => {
             }
         }
         addMiscItems(inventory, miscItemChanges);
-        const inventoryChanges: IInventoryChanges = {
-            ...updateCurrency(inventory, contributions.RegularCredits, false),
-            MiscItems: miscItemChanges
-        };
+        const inventoryChanges: IInventoryChanges = updateCurrency(inventory, contributions.RegularCredits, false);
+        inventoryChanges.MiscItems = miscItemChanges;
 
         if (techProject.ReqCredits == 0 && !techProject.ReqItems.find(x => x.ItemCount > 0)) {
             // This research is now fully funded.
diff --git a/src/services/inventoryService.ts b/src/services/inventoryService.ts
index cdf7bf5f..f4e48ca8 100644
--- a/src/services/inventoryService.ts
+++ b/src/services/inventoryService.ts
@@ -5,7 +5,7 @@ import {
 } from "@/src/models/inventoryModels/inventoryModel";
 import { config } from "@/src/services/configService";
 import { HydratedDocument, Types } from "mongoose";
-import { SlotNames, IInventoryChanges, IBinChanges, ICurrencyChanges } from "@/src/types/purchaseTypes";
+import { SlotNames, IInventoryChanges, IBinChanges, slotNames } from "@/src/types/purchaseTypes";
 import {
     IChallengeProgress,
     IConsumable,
@@ -26,8 +26,7 @@ import {
     ILibraryDailyTaskInfo,
     ICalendarProgress,
     IDroneClient,
-    IUpgradeClient,
-    ISlots
+    IUpgradeClient
 } from "@/src/types/inventoryTypes/inventoryTypes";
 import { IGenericUpdate } from "../types/genericUpdate";
 import {
@@ -127,13 +126,17 @@ export const combineInventoryChanges = (InventoryChanges: IInventoryChanges, del
             for (const item of right) {
                 left.push(item);
             }
-        } else if (typeof delta[key] == "object") {
-            console.assert(key.substring(-3) == "Bin");
-            console.assert(key != "InfestedFoundry");
-            const left = InventoryChanges[key] as IBinChanges;
-            const right = delta[key] as IBinChanges;
-            left.count += right.count;
-            left.platinum += right.platinum;
+        } else if (slotNames.indexOf(key as SlotNames) != -1) {
+            const left = InventoryChanges[key as SlotNames]!;
+            const right = delta[key as SlotNames]!;
+            if (right.count) {
+                left.count ??= 0;
+                left.count += right.count;
+            }
+            if (right.platinum) {
+                left.platinum ??= 0;
+                left.platinum += right.platinum;
+            }
             left.Slots += right.Slots;
             if (right.Extra) {
                 left.Extra ??= 0;
@@ -176,9 +179,9 @@ const occupySlot = (
         slotChanges.Slots -= 1;
     }
     updateSlots(inventory, bin, slotChanges.Slots, slotChanges.Extra);
-    return {
-        [bin]: slotChanges satisfies ISlots
-    };
+    const inventoryChanges: IInventoryChanges = {};
+    inventoryChanges[bin] = slotChanges satisfies IBinChanges;
+    return inventoryChanges;
 };
 
 export const addItem = async (
@@ -325,7 +328,7 @@ export const addItem = async (
             const inventoryChanges = addEquipment(inventory, weapon.productCategory, typeName);
             if (weapon.additionalItems) {
                 for (const item of weapon.additionalItems) {
-                    combineInventoryChanges(inventoryChanges, await addItem(inventory, item, 1));
+                    combineInventoryChanges(inventoryChanges, (await addItem(inventory, item, 1)).InventoryChanges);
                 }
             }
             return {
@@ -684,8 +687,8 @@ export const updateCurrency = (
     inventory: TInventoryDatabaseDocument,
     price: number,
     usePremium: boolean
-): ICurrencyChanges => {
-    const currencyChanges: ICurrencyChanges = {};
+): IInventoryChanges => {
+    const currencyChanges: IInventoryChanges = {};
     if (price != 0 && isCurrencyTracked(usePremium)) {
         if (usePremium) {
             if (inventory.PremiumCreditsFree > 0) {
diff --git a/src/services/purchaseService.ts b/src/services/purchaseService.ts
index cd6e7cad..2d1c66d3 100644
--- a/src/services/purchaseService.ts
+++ b/src/services/purchaseService.ts
@@ -164,7 +164,7 @@ export const handlePurchase = async (
                     addMiscItems(inventory, [invItem]);
 
                     purchaseResponse.InventoryChanges.MiscItems ??= [];
-                    (purchaseResponse.InventoryChanges.MiscItems as IMiscItem[]).push(invItem);
+                    purchaseResponse.InventoryChanges.MiscItems.push(invItem);
                 } else if (!config.infiniteRegalAya) {
                     inventory.PrimeTokens -= offer.PrimePrice! * purchaseRequest.PurchaseParams.Quantity;
                 }
@@ -191,11 +191,11 @@ const handleItemPrices = (
         addMiscItems(inventory, [invItem]);
 
         inventoryChanges.MiscItems ??= [];
-        const change = (inventoryChanges.MiscItems as IMiscItem[]).find(x => x.ItemType == item.ItemType);
+        const change = inventoryChanges.MiscItems.find(x => x.ItemType == item.ItemType);
         if (change) {
             change.ItemCount += invItem.ItemCount;
         } else {
-            (inventoryChanges.MiscItems as IMiscItem[]).push(invItem);
+            inventoryChanges.MiscItems.push(invItem);
         }
     }
 };
@@ -300,16 +300,14 @@ const handleSlotPurchase = (
 
     logger.debug(`added ${slotsPurchased} slot ${slotName}`);
 
-    return {
-        InventoryChanges: {
-            [slotName]: {
-                count: 0,
-                platinum: 1,
-                Slots: slotsPurchased,
-                Extra: slotsPurchased
-            }
-        }
+    const inventoryChanges: IInventoryChanges = {};
+    inventoryChanges[slotName] = {
+        count: 0,
+        platinum: 1,
+        Slots: slotsPurchased,
+        Extra: slotsPurchased
     };
+    return { InventoryChanges: inventoryChanges };
 };
 
 const handleBoosterPackPurchase = async (
diff --git a/src/types/purchaseTypes.ts b/src/types/purchaseTypes.ts
index f1e864be..e921d136 100644
--- a/src/types/purchaseTypes.ts
+++ b/src/types/purchaseTypes.ts
@@ -1,5 +1,5 @@
 import { IEquipmentClient } from "./inventoryTypes/commonInventoryTypes";
-import { IDroneClient, IInfestedFoundryClient, TEquipmentKey } from "./inventoryTypes/inventoryTypes";
+import { IDroneClient, IInfestedFoundryClient, IMiscItem, TEquipmentKey } from "./inventoryTypes/inventoryTypes";
 
 export interface IPurchaseRequest {
     PurchaseParams: IPurchaseParams;
@@ -22,20 +22,31 @@ export interface IPurchaseParams {
     IsWeekly?: boolean; // for Source 7
 }
 
-export interface ICurrencyChanges {
-    RegularCredits?: number;
-    PremiumCredits?: number;
-    PremiumCreditsFree?: number;
-}
-
 export type IInventoryChanges = {
     [_ in SlotNames]?: IBinChanges;
 } & {
     [_ in TEquipmentKey]?: IEquipmentClient[];
-} & ICurrencyChanges & {
-        InfestedFoundry?: IInfestedFoundryClient;
-        Drones?: IDroneClient[];
-    } & Record<string, IBinChanges | number | object[] | IInfestedFoundryClient>;
+} & {
+    RegularCredits?: number;
+    PremiumCredits?: number;
+    PremiumCreditsFree?: number;
+    InfestedFoundry?: IInfestedFoundryClient;
+    Drones?: IDroneClient[];
+    MiscItems?: IMiscItem[];
+} & Record<
+        Exclude<
+            string,
+            | SlotNames
+            | TEquipmentKey
+            | "RegularCredits"
+            | "PremiumCredits"
+            | "PremiumCreditsFree"
+            | "InfestedFoundry"
+            | "Drones"
+            | "MiscItems"
+        >,
+        number | object[]
+    >;
 
 export interface IAffiliationMods {
     Tag: string;
@@ -51,8 +62,8 @@ export interface IPurchaseResponse {
 }
 
 export type IBinChanges = {
-    count: number;
-    platinum: number;
+    count?: number;
+    platinum?: number;
     Slots: number;
     Extra?: number;
 };
@@ -69,18 +80,21 @@ export type SlotPurchaseName =
     | "TwoCrewShipSalvageSlotItem"
     | "CrewMemberSlotItem";
 
-export type SlotNames =
-    | "SuitBin"
-    | "WeaponBin"
-    | "MechBin"
-    | "PveBonusLoadoutBin"
-    | "SentinelBin"
-    | "SpaceSuitBin"
-    | "SpaceWeaponBin"
-    | "OperatorAmpBin"
-    | "RandomModBin"
-    | "CrewShipSalvageBin"
-    | "CrewMemberBin";
+export const slotNames = [
+    "SuitBin",
+    "WeaponBin",
+    "MechBin",
+    "PveBonusLoadoutBin",
+    "SentinelBin",
+    "SpaceSuitBin",
+    "SpaceWeaponBin",
+    "OperatorAmpBin",
+    "RandomModBin",
+    "CrewShipSalvageBin",
+    "CrewMemberBin"
+] as const;
+
+export type SlotNames = (typeof slotNames)[number];
 
 export type SlotPurchase = {
     [P in SlotPurchaseName]: { name: SlotNames; slotsPerPurchase: number };