My pet doesn't have its model applied

Are you using Model Engine 3.0.0 ? If so make sure that your models are in the correct folder for the Beta releases. All Model Engine files should now be located in "ModelEngine_Beta" folder instead of "ModelEngine", so make sure to move everything into the Beta folder and take the resource pack from here.

Otherwise, if everything is installed correctly (the .bbmodel files are in the blueprints folder of ModelEngine), then you are most likely using a free demo version of ModelEngine.

The free demo version which only allows a limited amount of models :

• If you want to keep using the demo version : remove some models that are working on your server in "./plugins/ModelEngine/blueprints" until you have less than 6 models in that folder.

• Recommended solution : buy the premium version of Model Engine.