Before installing the theme, please unzip "themeforest-xxxxxx-medz-medical-shopify-theme.zip" and upload the "medz.zip" file to Shopify to avoid the "layout/theme.liquid" missing template error.
Theme Extractions
Download the package from Themeforest.net (it will be in ZIP format).
Find the file "themeforest-xxxxxx-medz-medical-shopify-theme.zip" in your folder.
Extract the contents of the ZIP package you just downloaded.
Upload the medz.zip file to your Shopify store.
themeforest-xxxxxx-medz-medical-shopify-theme.zip
Upload Theme Through Shopify Admin Panel
Log in to the Shopify Panel.
Click "Online Store" from the left-hand menu.
Click "Add theme" > "Upload zip file."
Select and upload the medz.zip file. The theme will then be uploaded to your store.
Once the upload is complete, click "Actions" > "Publish."