php bin/magento module:enable WeltPixel_Backend --clear-static-content
Unknown module(s): 'WeltPixel_Backend'
If you are in the case above or similar there may be multiple reasons for it:
1. Extension Files are missing from the corresponding folder
2. Extension files are in the right folder but in .zip format. Files should be uncompressed like in the image below.
3. Folder structure is case sensitive, you should verify each folder name and make sure you are using the upper and lower case as presented in documentation
Pay attention at capital letters or spaces in 'WeltPixel' or extension name.
4.Make sure you are running the installation command in the root of your magento installation. Check a detailed article on this topic Here.