Yes, used different messages max sizes, with 2000 characters got the best speed but got the account banned, using 20000 is a great middle term and not banned for now, could get banned anyway, its an educational project

Could you try encoding data as images for better bandwidth (and probably worse latency)?

Images are often blocked on the free WhatsApp on airplanes

I wonder how that's implemented if all the traffic is encrypted. Presumably images are sent via a different domain or IP address?

Message size, perhaps.

And volume.

I was on a boat recently where WhatsApp was free to use, and you had to pay to use the rest of the internet. You could send and receive messages but attempting to send an image, which wasn’t even all that big in size, did not work on the free connection.

It must be either message size, or WhatsApp using a separate host name for attachments.

I would not be surprised if the free WA messaging is implemented by whitelisting the signaling ports and domains (XMPP or similar) which only handle text content and small inline attachments. While larger images are uploaded and fetched out of band (HTTP or similar) with only a URL or reference passing over the signaling channel.

They probably use some deep packet inspection on shore side firewall which blocks audio/video. Quite normal on congested satellite connections. Most “next-generation” firewall providers have predefined signatures for WhatsApp file transfer.

During the Facebook outage of a few years ago, WhatsApp messages still worked but I couldn't send an image. I think images are uploaded to Facebook-related servers add messages are through a separate real-time infrastructure, and it's likely that the message includes the fuzzy thumbnail and a url for the image from the other server.

Perhaps the client knows it’s on a free internet tire and blocks anything other than text.

Much easier to implement than encrypted package inspection.

Using less characters got you banned? I don't understand why that would happen. I would think using more characters would be more likely to get you banned since it's less like what normal users do.

Its in the README - it increases the the number of messages.

Well increasing the usage would also increase the number of messages.

How does Whatsapp choose to ban people? Total messages sent? Then increasing the message size doesn't stop you from being banned, it just makes it take longer before you're banned. Messages/second? Then avoiding the ban by a message restriction seems like a very clumsy way of doing it; it would be much more straightforward to avoid the ban by limiting the amount of messages/second.