Publish your derived project as Free Open Source Software (F.O.S.S) with AGPLv3 license with no limits. As a contributor citizen you can fork and redistribute echinopsii projects through AGPLv3. Your back-contribution on the echinopsii project source origin will always be much appreciated ;)
Pay the Free2Biz license yearly subscription if you wish to develop a proprietary or dual-licensed commercial derived project to fulfil your daily needs.
As an echinopsii user you must promote the echinopsii main developers' work and the Free2Biz license on any derived work redistribution (on-premise or XaaS). You must make a clear declaration that you are using an echinopsii project as a dependency and consequently your user may also have to request a Free2Biz license in their own work.
Finally, contribute your work back through git pull requests on echinopsii SCM through AGPLv3 and echinopsii CLA if you have modified any echinopsii source code to meet your needs.