Sage API comes with a Swagger tool that you can use to perform various "Try It Out" using GET, PATCH, POST and so on.  Once you load Sage 300 Web API in a supported browser you can open the Swagger UI.  The default URL is http://servername/sage300webapi. In your case you would be interested in playing with the following. Keep in mind that the Sage User you use to log in with must have been granted Web API permissions in the Sage security.  And, the ADMIN user does not have permissions by default, they have to be turned on in the Web and Web API config files.

Some examples here https://github.com/SageNADev/Sage300-SDK/tree/master/samples

If you've got access to the DPP forum, there are a few examples.

Hey Lee, did you get what you needed?  I too have a client with FileMaker databases and they are going to purchase Sage 300C (hosted in their office) and I am going to need to integrate.  Probably via Excel export / Import to start with.

Anyway, let me know if you found out any suitable info.  Thanks, Michael

If you're going to do this via excel import/export, use the templates provided. If you can export in that format, then all you need to do is run the import. If it is something you're going to be doing frequently, you can always create a macro to import the data.