Hi @Amir_Adel and welcome to the community!
Based off the error that’s being generated by postman, I believe this may have to do with an invalid API key being entered. Has the same key worked for your previously?
If not, can you try the testing again using a brand new Data API key?
I was able to reproduce the error on my test environment by providing an incorrect API key.
Please note that I was able to successfully perform the POST request to find a document before purposefully changing the API key to an invalid value:
Regards,
Jason