/**
 * Formats a number or string to a two-decimal string representation.
 * Validates the input is parseable to a number and throws MedusaError on NaN.
 *
 * @param amount - The amount to format (number or string)
 * @returns A string representation with exactly 2 decimal places
 * @throws MedusaError if the amount is not a valid number
 */
export declare function formatToTwoDecimalString(amount: number | string): string;