We can generate checksum error packets or traffic by using "Generate error" option (as shown below).
Add Raw or Bound StreamBlock-> Under "Frame" Tab-> Right click on "Checksum" field under "IPv4 Header"-> Click on "Generate Error" option.
Note: By this method we are generating IPv4 packets/traffic with checksum error. We also have other methods to generate errors in packets/traffic.
Note: DX/PX modules doesn't support to generate the checksum error on inner IPv4 headers, it can be achieved using MX/FX modules