Require payment for your core product rather than relying on optional monetization of free software
Free open-source with optional paid support, donations, or dual-licensing rarely generates meaningful revenue. Making payment mandatory (commercial license, required subscription) for your core product forces customers who get value to pay for it. Developers and businesses will use free software indefinitely without paying voluntarily.
When to use
When you have a useful product with active users but voluntary monetization (donations, optional licenses) generates negligible revenue
Don't do this
Relying on goodwill, donations, or dual-licensing to monetize software that companies depend on daily
1 Founder Who Did This
Spent 1.5 years with AGPL/MIT dual-licensing at 250 EUR/year, earning only 750 EUR total from 3 subscribers. Switched to commercial license requiring paid subscription to use the software