#The WARRIOR
rustic bloom
crisp hearth
you can't pass a PaymentIntent ID to Checkout
I don't really understand why you're using a PaymentIntent and a CheckoutSession here. If you're charging a saved card and you already know the pm_xxx ID, you would just use a PaymentIntent with it, and handle the outcome.
the docs for how to do that are here : https://stripe.com/docs/payments/save-during-payment?platform=web#charge-saved-payment-method
(1.) in payment intent which stays INCOMPLETE ue to 3DS authentication (and I can't do anything about it as it is in test mode)
that's not true — you can detect that it's happened by catching the exception, and then call https://stripe.com/docs/js/payment_intents/confirm_card_payment#stripe_confirm_card_payment-existing in the frontend to handle 3D Secure, that's all possible in test mode same as in live mode.