bapu4easy

MIT is a GPL compatible license. The license you have for the flipbook plugin is not GPL compatible.

“The Non-commercial and No Derivatives elements both conflict with the FSF’s free software definition, so no license that includes either of these is compatible with the GPL.”

See:
https://www.linux.com/news/trouble-artwork-and-free-software-licenses/

Looks like all of it needs to be under GPL. See: https://developer.www.ads-software.com/plugins/wordpress-org/detailed-plugin-guidelines/#1-plugins-must-be-compatible-with-the-gnu-general-public-license