Great Work !
curl -X POST https://www.oseamiya.tech/ -H "Authorization: Header" -H "Content-Type: application/json" -d "{\"key\" : \"value\"}"
I tried with this curl, however I think you didn’t added block to post the JSON text , like for me it should post this JSON : {"key" : "value"}
Result from the website :
I generated this CURL from reqbin,