Hi @krzysztow, welcome to the forum! 
Interesting bug, we tried looking into the API docs but it requires signing up for a demo. If you could share some of the docs, we could have a bit more context on what exactly is going on. It could be an issue with how one of the responses from the server is shaped, from looking at the response you are getting in the console, all of those keys are looking good. But as multiple request/response cycles are made in order to make OAuth work (setting up tokens in the process), one of the responses from the server may not be standardized to what Retool is expecting to be able grab the tokens. Otherwise, this should be working with your current settings.
Here is out troubleshoot guide you may have explored already. If so, it may be worth it to give it a shot at setting up Custom Auth. This way, we can have granular control of setting up the required variables fir the creation of this tokens.
Let us know if you have any questions! 