https://api.formcubes.com/submission/{your-form-ID}
<form method="POST" action="{put-your-form-endpoint-here}">
<input type="text" name="name">
<input type="email" name="email">
<input type="text" name="message">
<button type="submit">Submit</button>
</form>
action attribute of your HTML.
It will look something like this :
<form method="POST" action="https://api.formcubes.com/submission/{your-form-ID}">
<input type="text" name="name">
<input type="email" name="email">
<input type="text" name="message">
<button type="submit">Submit</button>
</form>