Explanation: It means that you don't have a "TextMeshPro" component on your GameObject.
Solution: Add a component that inherits from TMP_Text and then try again (you can add both the GUI or the 3DMesh one).
Please install the package "TextMeshPro", available in the Unity's package manager.
Please make sure you're using a newer version of the TextMeshPro package, starting from version "1.4.1" with Unity 2018.4.X or "2.1.3" for Unity 2019.4.X.
If you're using Unity 2019.x or above and the Editor is not loading global effects, be sure that you have "ProjectSettings/Editor/EnterPlayModeSettings → Reload Domain" set to true and enter playmode once.
Please close and reopen the Inspector tab, and restart the Unity Editor.
This is a bug on the Unity side and it seems to be fixed from the latest 2019.X and 2020.X versions. Read here for more.
P.S. If you're using 2019.X, you can fix it by also updating and importing the asset directly from the Asset Store.
Please be sure to read the Updating Guide and follow all the necessary steps.
Please be sure to read the Third Parties Integration guide and follow each related step.
If it still doesn't work, feel free to contact me.
Explanation: "TextAnimator" is inside the "Febucci.UI" namespace.
Solution: Be sure to include "using Febucci.UI;" at the top of your script.
This might happen if you have a large codebase, and TextAnimator wasn't initialized before setting the text. To fix this, please initialize TextAnimator when your game is loading (or similar), by calling
TAnimBuilder.InitializeGlobalData() (Scripting API).