There is no problem migrating from an ERL3 to an ER4because interfaces names between these routers are the same.

After migration, we have to manually create the interface eth3 (because eth3 doesn't exist on EdgeRouter Lite) like this :

configure
set interfaces ethernet eth3 speed auto
set interfaces ethernet eth3 duplex auto
commit
save

After that, reboot EdgeRouter a couple of times and everything will work perfectly.

There is no problem migrating from an ERL3 to an ER4 because interfaces names between these routers are the same.

After migration, we have to manually create the interface eth3 (because eth3 doesn't exist on EdgeRouter Lite) like this :

configure
set interfaces ethernet eth3 speed auto
set interfaces ethernet eth3 duplex auto
commit
save

After that, reboot EdgeRouter a couple of times and everything will work perfectly.