How to fix “Download failed. A valid URL was not provided.”?

If you get an error message Download failed. A valid URL was not provided. during plugin installation then It sounds like you are trying to install a plugin using TGM Plugin Activation from the child theme. In this case please:

• Temporary switch your theme to parent theme (WP Dashboard -> Appearance -> Themes) and then install recommended/required plugins.
• Switch back to your child theme and then activate these plugins again.

Installation and activation should work fine this way.

Notes: This is related to TGM Plugin Activation.