FCM.Net.MessageResponse Bad Request 400

[ullfindsmit]

I am trying to locate where this error is coming from to be able to debug.
I get this error without no context on what might have failed, and all my records show success.

Call Stack Trace: ErrorHandler at offset 755 in file:line:column <filename unknown>:0:0
MoveNext at offset 2357 in file:line:column <filename unknown>:0:0
RunInternal at offset 370 in file:line:column <filename unknown>:0:0
Run at offset 21 in file:line:column <filename unknown>:0:0
Run at offset 111 in file:line:column <filename unknown>:0:0
RunOrScheduleAction at offset 99 in file:line:column <filename unknown>:0:0
FinishContinuations at offset 1024 in file:line:column <filename unknown>:0:0
TrySetResult at offset 104 in file:line:column <filename unknown>:0:0
SetResult at offset 163 in file:line:column <filename unknown>:0:0
MoveNext at offset 335 in file:line:column <filename unknown>:0:0
RunInternal at offset 370 in file:line:column <filename unknown>:0:0
Run at offset 21 in file:line:column <filename unknown>:0:0
Run at offset 111 in file:line:column <filename unknown>:0:0
RunOrScheduleAction at offset 99 in file:line:column <filename unknown>:0:0
FinishContinuations at offset 1024 in file:line:column <filename unknown>:0:0
TrySetResult at offset 104 in file:line:column <filename unknown>:0:0
SetResult at offset 163 in file:line:column <filename unknown>:0:0
MoveNext at offset 557 in file:line:column <filename unknown>:0:0
RunInternal at offset 370 in file:line:column <filename unknown>:0:0
Run at offset 21 in file:line:column <filename unknown>:0:0
Run at offset 111 in file:line:column <filename unknown>:0:0
RunOrScheduleAction at offset 99 in file:line:column <filename unknown>:0:0
FinishContinuations at offset 1024 in file:line:column <filename unknown>:0:0
TrySetResult at offset 104 in file:line:column <filename unknown>:0:0
SetResult at offset 163 in file:line:column <filename unknown>:0:0
MoveNext at offset 945 in file:line:column <filename unknown>:0:0
RunInternal at offset 370 in file:line:column <filename unknown>:0:0
Run at offset 21 in file:line:column <filename unknown>:0:0
Run at offset 111 in file:line:column <filename unknown>:0:0
RunOrScheduleAction at offset 99 in file:line:column <filename unknown>:0:0
FinishContinuations at offset 1024 in file:line:column <filename unknown>:0:0
TrySetResult at offset 101 in file:line:column <filename unknown>:0:0
SetResult at offset 164 in file:line:column <filename unknown>:0:0
SetResult at offset 36 in file:line:column <filename unknown>:0:0
MoveNext at offset 386 in file:line:column <filename unknown>:0:0
RunInternal at offset 370 in file:line:column <filename unknown>:0:0
Run at offset 21 in file:line:column <filename unknown>:0:0
Run at offset 111 in file:line:column <filename unknown>:0:0
RunOrScheduleAction at offset 99 in file:line:column <filename unknown>:0:0
FinishContinuations at offset 1024 in file:line:column <filename unknown>:0:0
TrySetResult at offset 101 in file:line:column <filename unknown>:0:0
SetResult at offset 164 in file:line:column <filename unknown>:0:0
SetResult at offset 36 in file:line:column <filename unknown>:0:0
MoveNext at offset 877 in file:line:column <filename unknown>:0:0
RunInternal at offset 370 in file:line:column <filename unknown>:0:0
Run at offset 21 in file:line:column <filename unknown>:0:0
Run at offset 111 in file:line:column <filename unknown>:0:0
RunOrScheduleAction at offset 99 in file:line:column <filename unknown>:0:0
FinishContinuations at offset 1024 in file:line:column <filename unknown>:0:0
TrySetResult at offset 93 in file:line:column <filename unknown>:0:0
SetResult at offset 155 in file:line:column <filename unknown>:0:0
MoveNext at offset 367 in file:line:column <filename unknown>:0:0
RunInternal at offset 370 in file:line:column <filename unknown>:0:0
Run at offset 21 in file:line:column <filename unknown>:0:0
Run at offset 111 in file:line:column <filename unknown>:0:0
RunOrScheduleAction at offset 99 in file:line:column <filename unknown>:0:0
FinishContinuations at offset 1024 in file:line:column <filename unknown>:0:0
TrySetResult at offset 93 in file:line:column <filename unknown>:0:0
Complete at offset 53 in file:line:column <filename unknown>:0:0
CompleteFromAsyncResult at offset 147 in file:line:column <filename unknown>:0:0
Complete at offset 86 in file:line:column <filename unknown>:0:0
ProtectedInvokeCallback at offset 202 in file:line:column <filename unknown>:0:0
CompleteUserRead at offset 93 in file:line:column <filename unknown>:0:0
ParseTrailer at offset 226 in file:line:column <filename unknown>:0:0
ProcessResponse at offset 109 in file:line:column <filename unknown>:0:0
ReadCallback at offset 118 in file:line:column <filename unknown>:0:0
Complete at offset 86 in file:line:column <filename unknown>:0:0
ProtectedInvokeCallback at offset 202 in file:line:column <filename unknown>:0:0
ProcessFrameBody at offset 328 in file:line:column <filename unknown>:0:0
ReadFrameCallback at offset 172 in file:line:column <filename unknown>:0:0
CompleteRequest at offset 62 in file:line:column <filename unknown>:0:0
CheckCompletionBeforeNextRead at offset 40 in file:line:column <filename unknown>:0:0
ReadCallback at offset 127 in file:line:column <filename unknown>:0:0
Complete at offset 86 in file:line:column <filename unknown>:0:0
RunInternal at offset 370 in file:line:column <filename unknown>:0:0
Run at offset 21 in file:line:column <filename unknown>:0:0
Run at offset 85 in file:line:column <filename unknown>:0:0
Complete at offset 149 in file:line:column <filename unknown>:0:0
ProtectedInvokeCallback at offset 202 in file:line:column <filename unknown>:0:0
CompletionPortCallback at offset 293 in file:line:column <filename unknown>:0:0
PerformIOCompletionCallback at offset 132 in file:line:column <filename unknown>:0:0