Sorry for the late reply, when using the init string ATS0=1 the system doesn't load. i'm honestly not sure what's recommended, I got it to work (albeit very very briefly) with ATS0=1X1&C0&S0 at 2400 baud by doing trial and error from what was recommended by you for Proterm. Yes I have the manual but the only thing really recommended was different DIP switch settings on the Super Serial Card and that didn't fix the problem either. Also I noticed when using Proterm at 2400 baud the first command doesn't go through, there's a square character in front of the command on the OLED screen, maybe that has something to do with it? I took a pic, let me try and upload it.
EDIT: https://ibb.co/K9RQFvZ apologies for the low quality
EDIT2: with ATS0=1&C0 and ATS0=1&S0 gbbs loads and waits for a call, but when the call is made the system freezes.
EDIT3: I should also mention that before I got it working the first time, even when the init string wasn't right the system wouldn't freeze, there just wouldn't be a connection to the apple II, and when I closed the connection from the client side the apple II would make a noise indicating a disconnection and then would wait for the next call.
EDIT: https://ibb.co/K9RQFvZ apologies for the low quality
EDIT2: with ATS0=1&C0 and ATS0=1&S0 gbbs loads and waits for a call, but when the call is made the system freezes.
EDIT3: I should also mention that before I got it working the first time, even when the init string wasn't right the system wouldn't freeze, there just wouldn't be a connection to the apple II, and when I closed the connection from the client side the apple II would make a noise indicating a disconnection and then would wait for the next call.