Cashier Paddle Subscription swap error

According to the documentation on Changing Plans, to swap a subscription I did

$user->subscription()->swap($pricedId);

However, I am getting the error:

Paddle API error 'the new items are not valid for updating this subscription' occurred with validation errors ([{"field":"proration_billing_mode","message":"when changing the billing cycle only prorated_immediately, full_immediately or do_not_bill options are allowed"}])

I have tried doing

$user->subscription()->swap($priceId, [
        'proration_billing_mode' =>  'prorated_immediately'
    ])

But still gets the same error.

However, $user->subscription()->swapAndInvoice($priceId); works.

Anyone know what I am missing (if I am missing anything)?

I am using Cashier Paddle 2.x's