Laravel syncWithoutDetaching with extra fields

I am trying to save a simple belongsToMany relation into my database. First, my table:

    Schema::create('user_activity_log', function (Blueprint $table) {
        $table->unsignedBigInteger('activity_id');
        $table->unsignedBigInteger('log_id');
        $table->unsignedInteger('sets');
        $table->unsignedInteger('reps');
        $table->primary(['activity_id', 'log_id']);

        $table->foreign('activity_id')->references('id')->on('user_activities')
            ->onDelete('cascade')
            ->onUpdate('cascade');

        $table->foreign('log_id')->references('id')->on('user_logs')
            ->onDelete('cascade')
            ->onUpdate('cascade');
    });

My Log and Activity models have these relations:

Log:

public function activities()
{
    return $this->belongsToMany(Activity::class, 'user_activity_log', 'log_id', 'activity_id')->withPivot(['sets', 'reps']);
}

Activity:

public function logs()
{
    return $this->belongsToMany(Log::class, 'user_activity_log', 'activity_id', 'log_id')->withPivot(['sets', 'reps']);
}

When adding a new activity to an existing log, in my store method I am doing simply this:

$log->activities()->syncWithoutDetaching([
    $request->input('activity_id') => [
        'sets' => $request->input('sets'),
        'reps' => $request->input('reps')
    ]
]);

I am getting this error:

SQLSTATE[42S22]: Column not found: 1054 Unknown column 'id' in 'where clause' 

select * from `user_activity_log` where `id` = 0 limit 1

The data IS being saved though, so when I refresh the page and thus submit the form again, there are no errors. I cannot figure out why it is trying to find the id in the user_activity_log table.