Nice ! Do you only support some platforms (will love to know all supported platforms on your website)or can we also create images with counter based on external data sources (through an API)?
I think strange that you require a public URL to tranfert the audio file... That could be very complex for developers to first store audio file on a cloud provider, allow public access and then pass it to Hooho service.
Why not allowing to transfer data directly using an multipart/form-data or a base64 string?