I can't drop unique index

I have created unique index:

 $table->unique(['owner_id', 'promoter_id']);

and now i tray drop it

$table->dropUnique(['owner_id', 'promoter_id']);

General error: 1553 Cannot drop index 'connections_owner_id_promoter_id_unique': needed in a foreign key constraint (SQL: alter table connections drop index connections_owner_id_promoter_id_unique)

Also, i tried to drop foreign key before

$table->dropForeign('connections_promoter_id_foreign');

but still no results

via Chebli Mohamed