Integrity constraint violation Laravel 5.8 - laravel

Question

I have a ‘recurring_payments’ table
Schema::create('recurring_payments', function (Blueprint $table) {
$table->bigIncrements('id');
$table->string('user_id');
$table->string('card_id');
$table->string('day');
$table->integer('amount');
$table->timestamps();
});
I have a ‘card’ table
Schema::create('cards', function (Blueprint $table) {
$table->increments('id');
$table->unsignedInteger('user_id');
$table->string('token');
$table->string('last4');
$table->timestamps();
$table->softDeletes();
});
I have a ‘belongs to’ relationship between a ‘recurring_payment’ and a ‘card’
class RecurringPayment extends Model
{
protected $guarded = [];
public function card()
{
return $this->belongsTo(Card::class, 'token');
}
}
When I try to store the recurring payment
class Card extends Model
{
use SoftDeletes;
protected $fillable = [
'user_id',
'token',
'last4',
];
protected $hidden = [
'user_id',
'token',
'created_at',
'updated_at',
];
...
public function storeRecurringPayment($payment, $user)
{
$attributes = [
'user_id' => $user,
'card_id' => $payment->source['id'],
'day' => Carbon::now()->day()->addMonths(1)->format('d'),
'amount' => $payment->amount
];
// dd($attributes);
return $this->recurringPayment()->create($attributes);
}
public function recurringPayment()
{
return $this->hasOne(RecurringPayment::class);
}
...
}
it will not populate the ‘card_id’, it complains that the ‘card_id’ cannot be null, which is what I want, so far enough, but the ‘card_id’ is populated, this is the $attributes array died and dumped just before it's passed to the 'return $this->recurringPayment()->create($attributes);'
array:4 [▼
"user_id" => 3
"card_id" => "src_4zcdnrruvgxetpkgxocg6hhk5m"
"day" => "30"
"amount" => 10
]
I’m specifying in the ‘recurring_payment’ that I want to use ‘token’ as the foreign key not the default ‘card_id’ but I still get this error
SQLSTATE[23000]: Integrity constraint violation: 1048 Column 'card_id' cannot be null (SQL: insert into 'recurring_payments' ('user_id', 'card_id', 'day', 'amount', 'updated_at', 'created_at') values (3, ?, 30, 10, 2019-07-11 13:53:08, 2019-07-11 13:53:08))
Can anyone see the mistake I've made?