Japan Sandbox: Bookings API rejects writes with “Merchant subscription does not support write operations”

Questions
1

Hello Square Developer Support,

I’m testing an integration between an existing flower shop website’s pickup reservation form and Square Appointments in Japan.

The goal is to create a booking in Square from the form submission, linking the customer’s name and phone number and storing order details in the booking notes.

This is Sandbox testing only. I am not trying to process payments or change the production account.

Issue:
Booking creation fails with HTTP 403 and the message:
“Merchant subscription does not support write operations.”

The booking configuration also reports:
support_seller_level_writes: false

I attempted the Square Appointments Plus trial setup in Sandbox, but I have not confirmed that the required subscription entitlement was successfully activated.

Square Customer Support referred me to this developer forum.

Could you please clarify:

  1. Are seller-level booking write operations supported for Japanese Sandbox sellers?
  2. What exact steps enable the required Plus/Premium entitlement in Sandbox?
  3. If support_seller_level_writes remains false after onboarding, how can the account be investigated or corrected?
  4. Can this integration be tested entirely in Sandbox without starting a paid production subscription?

Please let me know which sanitized request/response details you need and how to locate the request ID.

Thank you.

3

Hi @tomu,

Square has a documented procedure for testing Appointments Plus and Premium in Sandbox.

1. Are seller-level writes supported for Japanese Sandbox sellers?

Yes

2. How do I enable the Sandbox subscription?

  1. Open the Developer Console → Sandbox test accounts.
  2. Choose Open beside the test account used by your integration.
  3. In that account’s Sandbox Dashboard, open Appointments and complete onboarding if needed.
  4. Choose Manage subscription, then select Appointments Plus or Premium.
  5. (Sometimes this does not appear in sandbox) Add the documented test payment method to prevent the Sandbox subscription from expiring after 30 days:
    • Card number: 4111 1111 1111 1111
    • CVV: 111
    • Expiration: 12/40
    • Name: any test name
    • Postal code: a test value appropriate for your locale
  6. Finally, the most important step:red_exclamation_mark:: Make sure you enable Online Bookings it is in the Appointements tab. Without this enabled you will still keep seeing the 403 error.

3. What if the flag remains false?

Send me a message here and I can help find a solution or workaround for this

4. Can testing stay entirely in Sandbox?

Yes, this type of testing can stay in Sandbox but there are a few functionalities that do not work in Sandbox, in cases where you reach those limitations you can test using production.

I hope this helps!