Laravel strings Foreign Key incorrectly formed

I'm trying to create a fk between tow tables. Here are my migrations:

 public function up()
    {
        Schema::create('contracts', function (Blueprint $table) {
            $table->increments('id');
            // Some other cols removed for this post
            $table->string('user_file_path');
            $table->timestamps();
            $table->foreign('user_file_path')->references('path')->on('user_files');
        });
    }

and

public function up()
    {
        Schema::create('user_files', function (Blueprint $table) {
            $table->increments('id');
            $table->integer('application_id')->unsigned();
            $table->string('random', 32);
            $table->string('path');
            $table->timestamps();
            $table->foreign('application_id')->references('id')->on('applications');
        });
    }

I get this error after running php artisan migrate

 General error: 1005 Can't create table 'dashboard'.'#sql-1890_b6' (errno: 150 "Foreign key constraint is incorrectly formed") (SQL: alter table 'contracts' add constraint 'contracts_user_file_path_foreign' foreign key ('user_file_path') references 'user_files' ('path'))

What am I doing wrong?

via Chebli Mohamed