Same Issue from the past 5 days. BingAI No longer works properly.

Sometimes the issue disappears but mostly it shows error:null

yeah same here! If using the SRCHLANG cookie.

I use _U cookie .. Whats srchlang cookie?

@WaterHyacinthInNANHU
It seems to be a problem on Microsoft's side. Sometimes a conversationSignature won't be returned when sending the conversation POST.
I don't experience the problem anymore after getting new optionSets and SliceIds from a vanilla request, however there still seems to be some problems on Microsoft's side, mainly InternalServiceErrors for normal POST requests.
So you might just see the error "Error processing request." displayed sometimes.
The issue isn't really related to the repo code itself, but we should leave it open until the errors disappear, so nobody creates a new issue.

@WaterHyacinthInNANHU It seems to be a problem on Microsoft's side. Sometimes a conversationSignature won't be returned when sending the conversation POST. I don't experience the problem anymore after getting new optionSets and SliceIds from a vanilla request, however there still seems to be some problems on Microsoft's side, mainly InternalServiceErrors for normal POST requests. So you might just see the error "Error processing request." displayed sometimes. The issue isn't really related to the repo code itself, but we should leave it open until the errors disappear, so nobody creates a new issue.

It is true that starting a new conversation solves this. Thanks for your timely help!

Yeah, it seems to have "solved itself" i.e. they fixed it on their end.
--Edit--
You'll still get the issue occasionally if you are not using the encrypted request and websocket.
So it's probably best to see #481 for a real fix.

I am getting this error out of the gate. I have not been able to get any successful responses, ever.
One thing that is different than the above error is that once I paste my cookies into settings.txt the error message changes from "|BingProdUnAuthenticatedUsers|" to "|BingProd|".