Cal. Rev. & Tax. Code § 55221.5

When an amount represented by a feepayer subject to this part to a customer as constituting reimbursement for fees subject to this part is computed upon an amount that is not taxable or is in excess of the fee amount and is actually paid by the customer to the feepayer, the amount so paid shall be returned by the feepayer to the customer upon notification by the State Board of Equalization or the customer that the excess has been ascertained. If the feepayer fails or refuses to do so, the amount so paid, if knowingly or mistakenly computed by the feepayer upon an amount that is not subject to the fee or is in excess of the fee amount, shall be remitted by that feepayer to this state. Those amounts remitted to the state by the feepayer shall be credited by the board on any amounts due and payable from the feepayer which are subject to this part and are based on the same activity, and the balance, if any, shall constitute an obligation due from the feepayer to this state.