How to use legacy key for rest api?

I’d like to update infusionsoft contacts and apply tags in our server’s background job.
I think it would be great if I can use legacy api key for rest api calls.

Is it possible?

You cannot use the Legacy API Key with the REST API:

Each request to the Infusionsoft REST API must include an Access Token . You may provide your token one of three different ways; we recommend providing your token as a Bearer token through an Authorization request header. This token is part of how we keep everyone safe.

https://developer.infusionsoft.com/docs/rest/

Cheers =]