To buy randoms, you must authorize the system account to sign a joint transaction to receive the result
cleos -u <address node> set account permission <user account> active quant.random --add-code
To purchase random it is necessary to perform a transaction with the transfer of QRNG tokens to the random contract
cleos -u <address node> push action quant.token transfer '["<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).