To purchase random it is necessary to perform a transaction with the transfer of QRNG tokens to the random contract
cleos-u<addressnode>pushactionquant.tokentransfer'["<sender>", "quant.random", "amount QRNG with config", "<account name for result forward>"]'-p<sender>
The amount (random_price) for the transfer can be seen in the contract config (example via cleos).