If you want to send requests to Make, your scenario needs to begin with a Custom Webhook trigger module. This will provide you with a URL that your server can call.
Hope this helps! Let me know if there are any further questions or issues.
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— @samliew
P.S.: Did you know, the concepts of about 70% of questions asked on this forum are already covered in the Make Academy. Investing some effort into it will save you lots of time and frustration using Make later!