According to NETS documentation for Frequency:
Indicates how often the merchant is allowed to make withdrawals based on the recurring agreement, in days. A recurring frequency of "1" will allow the merchant to make subsequent transactions on the card every day.
Minimum frequency is 0 day, meaning no limitation on the number of transactions per day. Maximum is 365 days.
Setting Frequency to 0 is not correct, because if there is a bug in PayPlans, you're risking to capture the customer money unlimited times, which is a huge drawback for us. I think this issue is related to bad error handling from your side, and a payment transaction should be handled carefully
It seems there are no grace period for bad transactions. According to PayPlans, the new transactions is being made every time CRON works, and since NETS is returning an error code, a new transaction is made. The most logical thing is to set this transactions that fails on hold.
Error handling in PayPlans is not good enough