.blend file is required.
You need to open it, go to the ActionEditor tab or usual Animation tab, and for every animation there You need to click an option called "Push Down" - small button near the title of animation/action. It sends animation to NonLinearAnimation Editor (NLA), which is also accessible as a separate Tab, but You don't need to open it or do anything there. Just push all of the animations down. When it is done, only then can animations be exported into .gltf.