The option to invest is for people who can save some part of their income. There is no need to consider saving if all you earn is what you need to survive. However, one can still increase his earnings by acquiring skills that can make him earn higher or seek other means of getting extra income.
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Investment must be with full awareness and control over one's finances. If they still have bills and needs to be met, then they must prioritize them and postpone their investment first. However, if they can allocate some of their money for investment, then they can do DCA to buy Bitcoin slowly in small amounts. Increasing income or reducing the amount of expenses can be an option for them to invest, but it must be done consistently to achieve maximum results.