Can't continue conversation after GPT-4o trial

Currently, whenever I start a new chat with ChatGPT it always uses the free trial of GPT-4o. (That in it of itself is not a problem.)

Whenever the trial runs out, it prompts me to either wait until the trial resets before continuing the same conversation, or start a new chat. I cannot send another message into the same chat. I remember previously it switched back between the newer model, and the one available for free users. It’s pretty annoying and I would much rather prefer it to switch to the lower version of the model after the trial goes on cooldown, allowing the conversation to continue.

If there is a reason behind this, please write it down in the replies. I’m open-minded and would accept any insight on this. ^^