Error Explanation Why it Happens How to Fix
Module '"../types"' has no exported member 'ApplyPromoResult'. TypeScript cannot find ApplyPromoResult in your types module. You either didn’t define it, or didn’t export it from your types/index.ts. Create ApplyPromoResult in a file (e.g., carts-inputs.ts) and export it in index.ts.

Example:
typescript <br> export type ApplyPromoResult = { <br> success: boolean; <br> discountAmount?: number; <br> message?: string; <br> }; <br>
The left-hand side of an arithmetic operation must be of type 'any', 'number', 'bigint' or an enum type.

'flashPrice' is possibly 'null'.		 TypeScript is complaining that flashPrice might be null and you’re trying to multiply it with item.quantity. TypeScript is strict about null or undefined values in arithmetic operations. Ensure flashPrice is always a number. Use a null check:

typescript <br> const price = flashPrice ?? 0; <br> newTotal += price * item.quantity; <br>
Property 'cart' does not exist on type '{ quantity: number; }'. You are trying to access item.cart but TypeScript thinks item has no cart property. Either the type of item is wrong, or cart is optional/missing in the type. Fix the type definition of item so cart exists, or add a safety check:

typescript <br> item.cart?.status === 'COMPLETED' <br>
Module '"./promo-codes"' declares 'DiscountType' locally, but it is not exported. TypeScript sees DiscountType in promo-codes.ts, but it is not exported, so your index.ts cannot re-export it. You imported it from Prisma but forgot to export it in promo-codes.ts. In promo-codes.ts, export it explicitly:

typescript <br> export { DiscountType }; <br>
Module '"../types"' has no exported member ... (other cart types) Same as the first error, TypeScript cannot find CreateCartInput, UpdateCartInput, etc. You didn’t define or export these types in your types/index.ts. Define each type in a file (like carts-inputs.ts) and export them via index.ts.

Written by A.M. Rinas