A chargeback notification is a structured record sent as an email, written for payment companies and lawyers. Five fields are always there: the dispute reason (the code on your notice), the transaction reference (ARN), the disputed amount, the response deadline and a submission portal URL. Read those first.
The dispute reason matters most because it sets which evidence can win. A 13.1 case turns on delivery records, a 10.4 case on evidence of the customer's relationship with you, and an 11.3 case on the timing of the bank approving the payment. The deadline is the field merchants miss most often, because the email gives an absolute date counted from a processing date it does not always show.
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The disputed amount and the ARN tell you which order is being argued and whether all of it or part of it is in dispute. The submission portal is the dashboard your payment company (Stripe, Shopify Payments and the like) expects you to use. A reply to the email, or a submission through Visa Resolve Online directly, will arrive too late or not at all.