When this happens
Either thisexternalPaymentObservationId was already accepted with different content, or a refund or reversal does not adjust the full related Payment. Payment observations are immutable. A refund or reversal must reverse the whole related Payment, and the total of all adjustments cannot exceed it.
What to do
Use a new ID for a different observation. For refunds and reversals, setamount to the full amount of the related Payment.