Geckolib API not showing

I am working on a mod when I heared about Geckolib and how we can make custom mob animations with it. I installed geckolib on mcreator and blockbench and made animations. But when I wanted to put the a procedure for animation and saved it, it showed an error and says that the geckolib animation block is not supported or something like that. I checked in preferences>plugins, the geckolib api was there. But it needed the api in external api. I had the geckolib api in the plugins but still I don't see anything in external api. And the problem is not with external api, its working fine with other api plugins, like patchouli, twilight forest, etc. Please help if anyone knows how to fix this