Studies being done in various European countries with universal basic income shows that it actually increases productivity, increases the creation of new businesses, and stimulates innovation. All of which helps the economy.
If you know that your basic needs will be met, then you are more likely to start a new business, take risks, go for that dream job that may not pay as much as your current job. Those who are disabled will be able to work part time without jeopardizing their disability checks, which will help them out of poverty.
And if your basic needs are taken care of, then more of your income is discretionary which supports and boosts the economy. It also puts the power in the workers hands, since the economic pressure to stay in a hostile workplace has been removed. It will force employers to treat their workers more fairly and actively create workplace environments conducive to retaining workers.