Well, the Individual Mandate required everybody to have health insurance, or pay a fine at the end of the year for each month you did not have health insurance. Here is an excerpt from an article describing why it is unconstitutional. "The 5th Circuit decided that the individual mandate as amended by the TCJA is unconstitutional. The court agreed with the state and individual plaintiffs and the federal government’s assertion that the requirement to produce some revenue is “essential” to the Supreme Court’s earlier finding in NFIB that the individual mandate could be saved as a valid exercise of Congress’s power to tax. Without that feature, the mandate is a command to purchase health insurance, which as the Supreme Court held in NFIB, is an unconstitutional exercise of Congress’ power to regulate interstate commerce." (https://www.kff.org/health-reform/issue-brief/explaining-california-v-texas-a-guide-to-the-case-challenging-the-aca/)
The key reason it had been found constitutional in previous cases was due to the power to tax, however, the Supreme Court is *California v. Texas* determined that although they have a power to create some revenue, they do not have the power to force people to buy health insurance, through the interstate commerce act.
