You can use this endpoint to submit the form:
https://docs.formaloo.net/#/operations/formDisplaysSlugSubmitCreate
In order to submit a form, you should send the fields and their values in the body. For example:
{
"{field_1_slug}": "Some Text", // Text field
"{field_2_slug}": 20, // Number field
"{field_3_slug}": "{selected_choice_slug}", // Choice field
"{field_4_slug}": [ "{selected_choice_1_slug}", "{selected_choice_2_slug}" ] // Multiple select field
}