Your logo won't be displayed on the Client Centre sign-in page for new clients until after they sign in for the first time.
The minimum size is 130 by 130px for square logos and 130 by 390px for rectangular logos.
The square logo option is only available if your firm is licensed for Advisory and Trial Balance.
Common image files supported include: JPG, JPEG, PNG, GIF, WEBP, ICO, and BMP.
There is not a maximum size for logo image files.