What is the best way to install an extension that has to be paid for on more than two computers? I am working in an educational context, and I am looking for a legal way to use extensions on a dozen computers or so.
You should probably check with the author to see if they have any limitations on the number of computers that you can install on with a single license. Most likely you would use the same download link for each one.
I am having this same issue with my computers and SketchUp Pro 2020.
Purchased an extension several years ago and between the several computers over the several years I am beyond the allowed number of instances of the extension. I am perfectly happy to purchase the additional licenses but the extension warehouse will not let me purchase it again or additional licenses.
This is an extension I use constantly that makes my work flow much faster.
Contact SketchUp support. They may be able to release licenses if you have computers you don’t use anymore.