"Resource not found of Type: ContactFlowId" - But it's right there. WhatsApp <-> Amazon Connect

I'm connecting WhatsApp to my Amazon Connect instance. And for that I'm following these steps as laid out in this AWS Blog: https://aws.amazon.com/blogs/contact-center/provide-whatsapp-messaging-as-a-channel-with-amazon-connect/

However, I get the following error:

"errorType": "ResourceNotFoundException", "errorMessage": "Resource not found of Type: ContactFlowId", "code": "ResourceNotFoundException", "message": "Resource not found of Type: ContactFlowId", "time": "2023-09-01T08:48:41.331Z", "requestId": "9a766769-a3ef-49b1-b8b4-8d9b02ba010b", "statusCode": 404,.

However the ContactFlowId that I'm sending appears to be correct. I added a bunch of console.log() statements to the code, and uploaded that, and it appears completely fine. The ContactFlowId is correct and exists in the Amazon Connect Instance.