How do you check that a crowdfunding platform is really licensed?

Check the platform's name against ESMA's official register of crowdfunding service providers. Lists published by industry associations are derived from that register, but the register itself is the primary source. A licensed platform can then offer its services across the EU without separate national licences.
For every project, a licensed platform must publish a key investment information sheet (KIIS). Read it before investing: it sets out the project, the risks and the terms in a standard format.
If a platform cannot be found in the register, or a project has no KIIS, treat it as unregulated.
A licence is a minimum standard, not a quality mark: it does not mean the projects are good or the forecasts are right. Capital is at risk: crowdfunding investments are not covered by deposit guarantee schemes, can lose part or all of their value, and may be hard to sell before the end of their term.