When updating data extensions via API and using Marketing Cloud APIs in general, note that the v1 endpoint was deprecated on August 1, 2019 and all new Marketing Cloud packages will need to use OAuth2.0 authentication.
Also depending on the Marketing Cloud edition purchased (Basic, Pro, Corporate, or Enterprise), there are limitations on the number of API calls per year. For example, Pro 2 million, Corporate 6 million, and Enterprise 200 million. Relevant post on Super Messages.
In terms of Rate Limiting, SOAP API calls are recommended to be less than 2,000 SOAP calls per minute and for REST API no more than 2,500 calls per minute.
Below are example endpoints to inserting data into a data extension asynchronously with REST API and creating a row in a data extension using a SOAP envelope.
Also here is an example of using Postman to test API Access Token Request.