You can work around this limitation by sending a POST request and including a query string parameter _HttpMethod to override the HTTP method.
For example, if you need to perform a PATCH requestyou can modify your request as follows by adding ?_HttpMethod=PATCH to the end of your url
POST /your/endpoint?_HttpMethod=PATCH
I found this solution in the Salesforce Developers Guide. Here’s a relevant excerpt:
If you use an HTTP library that doesn’t allow overriding or setting an arbitrary HTTP method name, you can send a POST request and provide an override to the HTTP method via the query string parameter _HttpMethod. In the PATCH example, you can replace the PostMethod line with one that doesn’t use override.
This approach allows you to use the PATCH HTTP method with N/https module in NetSuite.