The money Scott Lang attempted to steal by shrinking it with the prototype discs.
The Pym Discs were created by Henry Pym using Pym Particles. They are used to shrink things from a distance.
In To Steal an Ant-Man, Scott Lang stole Pym Discs along with the rest of Ant-Man's equipment; however, the discs were prototypes that caused objects to shrink until they entered a microverse, and Lang accidentally shrank four stacks of money into nothingness. Hank Pym used discs without this bug to shrink Scott's daughter Cassie to protect her from Cross.