Since current module release versions are outdated the official preffered way to install from master branch zip file does not work out of the box.
FIX:
Ensure zip file basename and root folder name inside zip have the same name as main module .php file (e.g. if omnivaltshipping.php is main file,
then zip filename must be "omnivaltshipping.zip" and root folder has to have name "omnivaltshipping").
PrestaShop v1.7.6 gives an error while installing module zip downloaded from official site: https://www.omniva.lt/verslo/siunta/sasajos_el_parduotuvems
Since current module release versions are outdated the official preffered way to install from master branch zip file does not work out of the box.
FIX: Ensure zip file basename and root folder name inside zip have the same name as main module .php file (e.g. if omnivaltshipping.php is main file, then zip filename must be "omnivaltshipping.zip" and root folder has to have name "omnivaltshipping").