How do I create a composite key?

create table "userWantList" (
  userId uuid references "userData" (id) primary key,
  "createdAt" timestamp default now(),
  "collectibleId" character not null primary key,
  "collectibleType" bigint references "collectibleTypes" (id)
);

create table "userWantList" (
  userId uuid references "userData" (id) primary key,
  "createdAt" timestamp default now(),
  "collectibleId" character not null primary key,
  "collectibleType" bigint references "collectibleTypes" (id)
);