What should be sent to the consumer when making a purchase in an online store?

Question

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What document do you need to prepare: check, invoice?
I was a little confused by the fact that Invoice is issued for payment, but when buying a ticket, after they sent me an e-ticket, they also sent an invoice three days later.
Thank you!

Answer 1

By law, a check is sufficient (for online payment), for good, a letter written in human language with the terms of the guarantee, receipt, and so on.