Looks like you’ve tried to follow a common path which some people suggest in attempt to save some money.
You buy a cheap Chinese no-name charger or just use some charger for an electric bike. It doesn’t work properly. You spend hours figuring out why it doesn’t work, read documentation, forums, etc. Then, you try to buy or borrow another cheap Chinese charger to test it once again. And it doesn’t work too.
Why not just buy an original charger which just works? It could’ve saved you money, time and possibly some nerves (depending on your character). Even if that Chinese charger worked, who knows if it’s suitable for LFP batteries and how it will affect the battery’s lifetime in the long run.
Just realize that the Bluetti AC200Max has the charging circuits built-in, whether by the DC port or the PV port. The powering device should not be a battery charger, just a plain DC power supply. None of the power input ports get a direct connection to the internal batteries.
Yeah that’s definitely the case about needing a dumb DC source rather than a charger with brains. However, I’ve read many times that AC charger input is directly connected to the battery though.
I admit that I have never heard that. It seems unlikely to me, since the included power supply is just a simple DC output, which is not how batteries are to be charged. Also, there is a BMS for the batteries which to my understanding is active in managing the battery charge and discharge cycles and reports the battery charge state, etc.