In case if you are not able to complete your monthly subscription payment on Netcore due to some problems with your Credit card then your the system would attempt the payment completion again on an everyday basis for next 2 days. During this time, you would be allowed to send emails with excess credits.
Please note that if your subscription payment is not completed even after 2 days, then your account would switch to a free plan with warmup limit of 100 emails/day. In this scenario, if you complete your payment request after wards then you can upgrade to better plan again but you would have to follow the warmup plan again and scale up your per day warmup limit for sending emails.