This error is presented to the customer when their wallet address has exceeded the permitted Transaction Score. Transaction scoring is a security feature that you have enabled.
For more information please see: Transaction Scoring
The explanation (to the customer) is vague by design.
Solution: the wallet has been flagged by the provider, it is recommended that you explain the situation to the customer, but ultimately - the choice is entirely up to you how you proceed.
Manually send the coin to the target wallet, or
refund the customer.