Must have this adapter for the R6 Mk II to use a legacy flash like the 600EX-RT, or Godox V860 II

Helping transition to Canon cameras featuring a Multi-Function Shoe, the AD-E1 Multi-Function Shoe Adapter adapts legacy Speedlite accessories to the updated Multi-Function Shoe design. Ideal for Speedlites and shoe-mounted accessories like the EL-1, 600EX II-RT, ST-E3-RT, OC-E3 Flash Cord, and others, this adapter maintains a complete weather-sealed design and provides a secure connection to current updated shoe type.

This adapter can also be used with other shoe-mounted accessories, such as shotgun mics or on-camera lights, and features dual-locking pins on the Multi-Function Shoe side for a secure attachment.