The Service Invoice, as the name already suggests, is used when the transaction involves not the purchase and sale of a physical commodity, but the provision of a service. In addition to registering the description of the services, it includes the ISS (Service Tax).
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Its issuance can be destined to a legal or natural person and happens with the RFB (Brazilian Federal Revenue) or the city hall where the company or entrepreneur is registered. Because it is simpler and more flexible, it is usually the type applied to MEIs and small businesses.