Mirage should be compatible with SpongeAPI 7.1.4. The problem is not here. There is an incompatibility with elytradev's mod. Download the jar files here instead of on the ore page, this should fix your issue, if it's not the case you can comment this issue: #11 .
The plugin is written for API 7.1.0, on the server is API 7.1.4, so she crush? Perhaps conflict mods. Without plugin everything works fine.
crash-2018-11-09_15.15.50-server.txt latest.log
SPONGE 1.12.2-2768-7.1.4 FORGE 1.12.2-14.23.5.2768