Minimal Requirements:
Quick installation with WordPress already installed:
Step 1:
You should have WordPress >=5.6 installed ( https://wordpress.org/ ), best if you have a clean installation.
Step 2:
Upload shelly.zip on the server via Cpanel file manager to folder “wp-content/themes” or install it via Appearance>Themeы>Add Theme
Step 3:
Open your WordPress Administration, click on Appearance and Activate the Shelly theme.

Step 4:
Install the required plugins

If you run into issues such as white screen, your demo import fails or takes a long time, it’s not imported completed, and other similar issues are all related to low PHP configuration limits. Check the Recommended PHP Configuration Limits
Follow The Easy Steps

Go to Appearance>Customize to set up the theme color and typography.
Appearance> Customize> Colors>Global colors settings allow to customize Site Background, Primary and Text color, and other related options.
Appearance> Customize> Colors>Text Selection settings allow to customize the text color on highlighting.
Appearance> Customize> Typography>General Fonts allows you to customize the primary and secondary font family, size, line height, etc.
Appearance> Customize> Typography>Heading Options allows you to customize the font family, size, line height for all types of headings.
Appearance> Customize> Typography>Blockquote Options allows you to customize the font family, size, line height, Letter Spacing for the Blockquote blocks.
Appearance> Customize> Typography>Button Options settings customize fonts for the button.
Appearance> Customize> Typography>Input Options settings configure options related to fonts for input text.
Elementor is a page builder plugin that replaces the basic WordPress editor with a live frontend editor, so you can create complex layouts visually, and design your website live, without having to switch between the editor and the preview mode.
There are available custom Elementor widgets of the Shelly theme to help you quickly create a block with specific functionality. Edit with Elementor any page to use the provided elements.

The theme also contains custom WordPress widgets that can be used in the page sidebar or footer. Go Appearance>Widgets to use the Shelly widgets

The list of custom theme widgets
There are three types of custom post types available once the Shelly theme is activated:
Each of the types has extra fields to display the necessary information.
If you get a 404 error on the front end in any custom post type go to Settings>Permalinks and switch the settings to Post name.

WordPress.com doesn’t allow you to upload your own themes (you’re stuck with what’s available for free or in their marketplace) so in order to use any of the awesome themes on the marketplace, you’ll need to get yourself a self-hosted installation of WordPress.
We will try to make as most features possible compatible but they have so many limitations for plugins that are not suggested to use it.
Please make sure you are trying to install the correct package. Unzip the downloaded archive from ThemeForest and find the correct installation package in the “Theme” folder.
Check this articles:
https://superpctricks.com/the-link-you-followed-has-expired-wordpress-error/
So this usually happens because of the small upload_max_size configuration on the server and is easy to solve. You can also extract the theme directly on the server CPanel file manager into the folder “wp-contentthemes” instead of uploading via a dashboard.
This sometimes happens in WordPress, not related to a theme, Clear your browser cache and cookies or use another browser / PC.
Also use the clean latest WordPress version, because some third-party plugins can also cause issues.
Check above, similar to link has expired.
Also, check your PHP version, must be min. 5.6 or above.