There can be a few reasons.
Usually, it’s because you don’t have enough money associated to the currency pocket from which the Direct Debit was set from. Funds MUST be on the same currency account that was used for setting up Direct Debit (ex: for a GBP Direct Debit, you have to have enough funds on the GBP currency pocket whose details you provided to the merchant to set it up).
Worth double checking with the merchant if they have your correct account details: for GBP it is your GBP account number and sort code, for EUR - your EUR IBAN and BIC code.
The limit of the volume of a single EURO Direct Debit payment is 10,000 EUR. There is no limit for GBP Direct Debit.
Make sure the beneficiary is setting up a Core DD scheme, as we do not support B2B just yet!
If your Direct Debit is still failing, contact our support team, and we’ll be happy to help.