What are the options for Rest?

Pedro, an API does not necessarily have to be Web or follow any standards that are widely accepted by the community, such as SOAP or REST.

For example, if you are a .NET programmer, you can create a service that receives or sends fixed-text text files over a TCP port, you will have a communication interface between the service and whatever application the consume.

However, if we were talking about WebServices, a REST API would be the most friendly way to make your service available.

If your service is consumed by applications from a variety of sources, the SOAP standard will give you more tools to validate the request format, forms of authentication, security used in the transport layer, order of the methods call the service, use a transaction (Database) of the client within your service, in addition to other possibilities.