curl --request POST \
--url https://api.cal.id/slots/reserve \
--header 'Authorization: Bearer <token>' \
--header 'Content-Type: application/json' \
--data '
{
"eventTypeId": 123,
"slotStart": "2026-05-02T10:00:00.000Z"
}
'import requests
url = "https://api.cal.id/slots/reserve"
payload = {
"eventTypeId": 123,
"slotStart": "2026-05-02T10:00:00.000Z"
}
headers = {
"Authorization": "Bearer <token>",
"Content-Type": "application/json"
}
response = requests.post(url, json=payload, headers=headers)
print(response.text)const options = {
method: 'POST',
headers: {Authorization: 'Bearer <token>', 'Content-Type': 'application/json'},
body: JSON.stringify({eventTypeId: 123, slotStart: '2026-05-02T10:00:00.000Z'})
};
fetch('https://api.cal.id/slots/reserve', options)
.then(res => res.json())
.then(res => console.log(res))
.catch(err => console.error(err));<?php
$curl = curl_init();
curl_setopt_array($curl, [
CURLOPT_URL => "https://api.cal.id/slots/reserve",
CURLOPT_RETURNTRANSFER => true,
CURLOPT_ENCODING => "",
CURLOPT_MAXREDIRS => 10,
CURLOPT_TIMEOUT => 30,
CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
CURLOPT_CUSTOMREQUEST => "POST",
CURLOPT_POSTFIELDS => json_encode([
'eventTypeId' => 123,
'slotStart' => '2026-05-02T10:00:00.000Z'
]),
CURLOPT_HTTPHEADER => [
"Authorization: Bearer <token>",
"Content-Type: application/json"
],
]);
$response = curl_exec($curl);
$err = curl_error($curl);
curl_close($curl);
if ($err) {
echo "cURL Error #:" . $err;
} else {
echo $response;
}package main
import (
"fmt"
"strings"
"net/http"
"io"
)
func main() {
url := "https://api.cal.id/slots/reserve"
payload := strings.NewReader("{\n \"eventTypeId\": 123,\n \"slotStart\": \"2026-05-02T10:00:00.000Z\"\n}")
req, _ := http.NewRequest("POST", url, payload)
req.Header.Add("Authorization", "Bearer <token>")
req.Header.Add("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)
defer res.Body.Close()
body, _ := io.ReadAll(res.Body)
fmt.Println(string(body))
}HttpResponse<String> response = Unirest.post("https://api.cal.id/slots/reserve")
.header("Authorization", "Bearer <token>")
.header("Content-Type", "application/json")
.body("{\n \"eventTypeId\": 123,\n \"slotStart\": \"2026-05-02T10:00:00.000Z\"\n}")
.asString();require 'uri'
require 'net/http'
url = URI("https://api.cal.id/slots/reserve")
http = Net::HTTP.new(url.host, url.port)
http.use_ssl = true
request = Net::HTTP::Post.new(url)
request["Authorization"] = 'Bearer <token>'
request["Content-Type"] = 'application/json'
request.body = "{\n \"eventTypeId\": 123,\n \"slotStart\": \"2026-05-02T10:00:00.000Z\"\n}"
response = http.request(request)
puts response.read_body{
"success": true,
"data": {
"eventTypeId": 100482,
"slotStart": "2026-05-04T09:00:00.000Z",
"slotEnd": "2026-05-04T09:15:00.000Z",
"slotDuration": 15,
"reservationUid": "3f0b7c92-4a1e-4d6b-9c2f-7a5e1b8d0c34",
"reservationDuration": 5,
"reservationUntil": "2026-05-01T12:05:00.000Z"
},
"message": "Slot reserved"
}{
"success": false,
"message": "<string>",
"error": {
"code": "<string>",
"message": "<string>",
"details": "<unknown>"
}
}{
"success": false,
"message": "<string>",
"error": {
"code": "<string>",
"message": "<string>",
"details": "<unknown>"
}
}{
"success": false,
"message": "<string>",
"error": {
"code": "<string>",
"message": "<string>",
"details": "<unknown>"
}
}{
"success": false,
"message": "Rate limit exceeded",
"error": {
"code": "TOO_MANY_REQUESTS",
"message": "Too many requests. Please retry after the rate limit window resets."
}
}{
"success": false,
"message": "<string>",
"error": {
"code": "<string>",
"message": "<string>",
"details": "<unknown>"
}
}Reserve a slot
Puts a temporary hold on a slot so a booker can finish filling in a form without losing the time. Send eventTypeId and slotStart; the response returns data.reservationUid — note the field is reservationUid, not uid — along with slotStart, slotEnd and reservationUntil. The hold lasts 5 minutes by default; pass reservationDuration to change it. Important: reserving does not check availability, so a 200 here is not a guarantee — POST /booking/ can still fail for that time.
curl --request POST \
--url https://api.cal.id/slots/reserve \
--header 'Authorization: Bearer <token>' \
--header 'Content-Type: application/json' \
--data '
{
"eventTypeId": 123,
"slotStart": "2026-05-02T10:00:00.000Z"
}
'import requests
url = "https://api.cal.id/slots/reserve"
payload = {
"eventTypeId": 123,
"slotStart": "2026-05-02T10:00:00.000Z"
}
headers = {
"Authorization": "Bearer <token>",
"Content-Type": "application/json"
}
response = requests.post(url, json=payload, headers=headers)
print(response.text)const options = {
method: 'POST',
headers: {Authorization: 'Bearer <token>', 'Content-Type': 'application/json'},
body: JSON.stringify({eventTypeId: 123, slotStart: '2026-05-02T10:00:00.000Z'})
};
fetch('https://api.cal.id/slots/reserve', options)
.then(res => res.json())
.then(res => console.log(res))
.catch(err => console.error(err));<?php
$curl = curl_init();
curl_setopt_array($curl, [
CURLOPT_URL => "https://api.cal.id/slots/reserve",
CURLOPT_RETURNTRANSFER => true,
CURLOPT_ENCODING => "",
CURLOPT_MAXREDIRS => 10,
CURLOPT_TIMEOUT => 30,
CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
CURLOPT_CUSTOMREQUEST => "POST",
CURLOPT_POSTFIELDS => json_encode([
'eventTypeId' => 123,
'slotStart' => '2026-05-02T10:00:00.000Z'
]),
CURLOPT_HTTPHEADER => [
"Authorization: Bearer <token>",
"Content-Type: application/json"
],
]);
$response = curl_exec($curl);
$err = curl_error($curl);
curl_close($curl);
if ($err) {
echo "cURL Error #:" . $err;
} else {
echo $response;
}package main
import (
"fmt"
"strings"
"net/http"
"io"
)
func main() {
url := "https://api.cal.id/slots/reserve"
payload := strings.NewReader("{\n \"eventTypeId\": 123,\n \"slotStart\": \"2026-05-02T10:00:00.000Z\"\n}")
req, _ := http.NewRequest("POST", url, payload)
req.Header.Add("Authorization", "Bearer <token>")
req.Header.Add("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)
defer res.Body.Close()
body, _ := io.ReadAll(res.Body)
fmt.Println(string(body))
}HttpResponse<String> response = Unirest.post("https://api.cal.id/slots/reserve")
.header("Authorization", "Bearer <token>")
.header("Content-Type", "application/json")
.body("{\n \"eventTypeId\": 123,\n \"slotStart\": \"2026-05-02T10:00:00.000Z\"\n}")
.asString();require 'uri'
require 'net/http'
url = URI("https://api.cal.id/slots/reserve")
http = Net::HTTP.new(url.host, url.port)
http.use_ssl = true
request = Net::HTTP::Post.new(url)
request["Authorization"] = 'Bearer <token>'
request["Content-Type"] = 'application/json'
request.body = "{\n \"eventTypeId\": 123,\n \"slotStart\": \"2026-05-02T10:00:00.000Z\"\n}"
response = http.request(request)
puts response.read_body{
"success": true,
"data": {
"eventTypeId": 100482,
"slotStart": "2026-05-04T09:00:00.000Z",
"slotEnd": "2026-05-04T09:15:00.000Z",
"slotDuration": 15,
"reservationUid": "3f0b7c92-4a1e-4d6b-9c2f-7a5e1b8d0c34",
"reservationDuration": 5,
"reservationUntil": "2026-05-01T12:05:00.000Z"
},
"message": "Slot reserved"
}{
"success": false,
"message": "<string>",
"error": {
"code": "<string>",
"message": "<string>",
"details": "<unknown>"
}
}{
"success": false,
"message": "<string>",
"error": {
"code": "<string>",
"message": "<string>",
"details": "<unknown>"
}
}{
"success": false,
"message": "<string>",
"error": {
"code": "<string>",
"message": "<string>",
"details": "<unknown>"
}
}{
"success": false,
"message": "Rate limit exceeded",
"error": {
"code": "TOO_MANY_REQUESTS",
"message": "Too many requests. Please retry after the rate limit window resets."
}
}{
"success": false,
"message": "<string>",
"error": {
"code": "<string>",
"message": "<string>",
"details": "<unknown>"
}
}Authorizations
Use the Authorization header with Bearer scheme.
Examples:
- API Key: Authorization: Bearer calid_xxxxx
Body
Event type identifier for the slot reservation.
x > 1123
Slot start time in ISO-8601 format with timezone offset.
"2026-05-02T10:00:00.000Z"
Optional duration in minutes. Can be sent as a number or numeric string and must match event type allowed durations when configured.
^[1-9]\d*$"30"
Optional reservation hold duration in minutes. Defaults to 5 when omitted and requires authenticated requests.
x > 110
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