Amount of tokens in ETH, as a decimal string (e.g. "0.925413332702449273"). Send it as a JSON string to preserve full 18-decimal precision; a JSON number loses precision before it reaches the server. Must be a plain positive decimal of at least 0.01 ETH with no more than 18 fractional digits; exponential notation (e.g. "1e-2") and signs are rejected with a 400 validation error.