Configure the MLAG port facing the downstream device as LACP. Enter the following command on the MLAG switch:
enable sharing <master port#> grouping <port list> algorithm lacp
Alternately, if you want to use static LAG links, you can configure the downstream switch LAG as a static LAG instead of LACP. This will make both sides of the LAG link be static.
enable sharing <master port#> grouping <port list>