It's generally on the honor system. Having to pay for certain usages is likely in their terms of service so they could theoretically sue you if you didn't have

It's generally on the honor system. Having to pay for certain usages is likely in their terms of service so they could theoretically sue you if you didn't have a license. Big companies will pay to be legal. Or to get a support package. Small companies will probably pay out of honor. Some people won't pay but most of them probably wouldn't pay if forced anyway. I support a UI framework that is just an npm package. I could theoretically use it for free, I just wouldn't get support. I pay because it's the right thing to do and it's not very expensive.