Manjaro -invalid or corrupted package.

I came across an error during a regular update saying:

"invalid or corrupted package (PGP signature)"

A bit of digging suggested many solutions, which were tried, but made no difference. I still couldn't complete an update.

Eventually, from the manjaro forum, a post suggested the following commands - the order is very important:

sudo pacman-key --init 

sudo pacman-key --populate archlinux manjaro

sudo pacman-key --refresh-keys

This returned the system to normal and the update completed successfully.