I made a paint can shaker for my cheap aliexpress massage gun.

The gland end of the shaker tool that goes into the massage gun is 12,7mm in diameter.
I secure the can with a rubber band and put some grip tape on the inside of the holder to keep the can from sliding due to the vibration.
The tool is made to fit 66mm paint cans.

Also i reused the rubber bushing from an attachment that came with the gun but i included a model of one if anyone wants to print it out in TPU.