What happens if the submitter enters wrong credit card details?

i haven't integrated paypal into my form yet so i cannot test it for myself. 

but i wanted to ask:

1. lets say that by mistake the applicant have insert a wrong credit card number and the payment wasn't successful. will the applicant get a notice right away or will it let him continue and submit the form? (and will direct him to the thank you page as it was submitted?) 
   - (from the the FAQ i understood it won't send him the notification email right?)

2. in such case, how can the submitter complete the payment after clicking the submit button? (without retyping and submitting the whole form again) 

If you are integrating PayPal standard or Express your submitters are not asked for credit card details, but are instead sent to PayPal to make the payment.

This means that PayPal will notify them of any issues with the credit card entered.

Once they make the payment they are taken to Thank you page and sent the autoresponder email.

If you use PayPal Pro, it will have the option to ask for credit card details (like some of our other integrations). Such integrations validate the data so they should not be able to submit without providing the correct details.

Do let us know if you happen to have any additional questions and we would be happy to assist with the same.

I would however suggest checking out the following guides:

Setting Up Your First Order Form

PayPal Forms

Difference Between PayPal & PayPal Pro