Use mandatory license keys with hard enforcement to convert free open source users to paid customers overnight
When pivoting from free open source to commercial, implement a hard license key requirement that stops the application from functioning without a valid key. This forces a binary decision: pay or stop using. Combined with source-available code (visible but not free to run), this creates immediate conversion pressure without losing the trust benefits of open code.
When to use
When you have an established open source project with real users but near-zero revenue, and you own the copyright (via CLA or sole authorship)
Don't do this
Using honor-system licensing or soft enforcement that allows users to continue running without paying indefinitely
1 Founder Who Did This
Switched from AGPL (free) to commercial license with mandatory key. App stops working 15 minutes after startup without valid key. Previously free users were forced to decide: pay or stop using.