1. Open Unity
2. On top of Unity window, you will see your version number. Will look something like, Unity 2020.3.8f1
3. Go to: https://github.com/Unity-Technologies/2d-extras
4. On Unity 2d Extras Github, check to see if your Unity version above matches the current branch. If you're unsure, do Control + F and search the word Branches to find the branches link on Github, click this. This will take you to all the branches of 2d extras.
5. Select the branch that matches your Unity Version. Ex: If my version is 2020.3, I would select the 2020.3 branch. Click the blue link to your branch.
6. Click the green code button on top right of the branch page, download zip.
7. Extract the zip folder once downloaded.
8. Open your Unity project, go to Window -> Package Manager.
9. Click the + in package manager, select Add package from disk.
10. Locate your unzipped folder for 2d extras and select the package.json inside it, click open.
11. The package will load into your project... fingers crossed error-free.
12. Rejoice.

Note: If this didn't work, you most likely downloaded the incorrect version from Github. Also make sure you deleted the prior 2d extras package from your Unity project that was giving you errors if you had one.

1. Open Unity
2. On top of Unity window, you will see your version number. Will look something like, Unity 2020.3.8f1
3. Go to: https://github.com/Unity-Technologies/2d-extras
4. On Unity 2d Extras Github, check to see if your Unity version above matches the current branch. If you're unsure, do Control + F and search the word Branches to find the branches link on Github, click this. This will take you to all the branches of 2d extras.
5. Select the branch that matches your Unity Version. Ex: If my version is 2020.3, I would select the 2020.3 branch. Click the blue link to your branch.
6. Click the green code button on top right of the branch page, download zip.
7. Extract the zip folder once downloaded.
8. Open your Unity project, go to Window -> Package Manager.
9. Click the + in package manager, select Add package from disk.
10. Locate your unzipped folder for 2d extras and select the package.json inside it, click open.
11. The package will load into your project... fingers crossed error-free.
12. Rejoice.

Note: If this helped, give this an upvote. If this didn't work, you most likely downloaded the incorrect version from Github. Also, make sure you deleted the prior 2d extras package from your Unity project that was giving you errors if you had one as this could cause file conflictions.