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Dear developers,
we would like to make a recommendation for the use of the TPP Rejection-NoFunds Preferred Flag.
Before submitting a payment the current balance is checked. To ensure that the payment will be processed, the TPP can add the header TPP-Rejection-NoFunds-Preferred within the payment initiation to request that the payments must be automatically rejected if funds are not available.
Further information on this can be found here: https://psd2.developer.commerzbank.com/content/howto/pis-initiate-payment 
If you have any further questions about this, please feel free to contact PSD2 support at any time.
Your Commerzbank Support Team