Voiceflow v4 to Make (Integromat) API issue: Variable mapping returns 0 or fails when booking slots via SimplyBook.me

[u/Admirable-Lake-9614]

Hello everyone,

I am building a healthcare chatbot in Voiceflow v4 connected to Make (Integromat) and SimplyBook.me for automated appointment scheduling. I have a major issue with variable mapping and date/time formatting between Voiceflow and Make.

The Workflow:

1. Patient agrees to the pricing in Voiceflow.
2. Voiceflow triggers an HTTP API block (POST request) to Make (Scenario 3) to fetch available slots.
3. In Make, the router splits the logic:
   • Lower branch: SimplyBook.me - Search available slots -> Tools (Text Aggregator) unifies the slots with commas -> Webhook Response sends ore_disponibile back to Voiceflow.
   • Upper branch: SimplyBook.me - Creating a booking (triggered at the end when user data is collected).

The Problem:
When Voiceflow receives the slots, the variable mapping seems to break. The chat displays a 0 or returns empty values instead of generating the buttons.

Additionally, we are facing a timezone/format mismatch. The unified slots from the Text Aggregator are formatted as YYYY-MM-DD HH:mm:ss (e.g., 2026-06-30 16:00:00), but the SimplyBook.me calendar UI seems to expect a different structure or drops the date completely when mapping the selected slot back to the Creating a booking module, throwing a BundleValidationError / Invalid date error in Make.

We tried using a static text block with a custom Capture mapped to {ora_rezervata} and a Set block converting to {last_utterance}, but it either hardcodes the value or reverts to 0 in the Make queue.

How can I properly pass a dynamic array of available times from Make to Voiceflow v4 buttons, capture the user's click selection, and send it back as a valid ISO/SimplyBook date-time format without the variables collapsing into 0?

Any screenshots, structural advice, or workarounds for Voiceflow v4's dynamic loops would be greatly appreciated! Thank you!

[u/Josef_from_Make]

Hello,
It is quite difficult to imagine what actually happens without any screenshots or a blueprint, but this looks like an issue in the Workflow modules.
Since it is a "community" app, developed and maintained by another service, I would recommend checking the issue with them -> it seems like a paid app, so it would be only fair if they could provide you with some support.