How to add a promotion for selected products by a specific percentage without a discount code? so that the website displays the previous and promotional prices at once?
Why don’t you use the list price?
I wanted to set up a promotion 2-3 of the entire offer (about 700 products). Changing it manually will be time-consuming.
Then you need a plugin or change the prices with the Admin-API and a own Script.
Are there any free plugins available?
I do not think so, but I do not know for sure.