American Express Reason Code R03

Amex says the merchant's previous response to a dispute didn't include enough information to resolve it.

A prior chargeback response was submitted but lacked the specific documentation Amex needed to make a determination.

This is a second chance — read exactly what's missing from the original request and supply it directly.

Whatever specific documentation Amex's request says is missing from your original response.

Submitting a generic response instead of addressing the exact evidence Amex asked for.