After coming across this while I was trying to “fix” things, let me write you guys something that might solve a few problems: triple- or quadruple-check if your data is correct. n8n mumbles something about a refreshToken, but that’s not the issue. Under the hood, your input data was wrong. I for example was entirely sure that I put in the correct ID for the space I wanted to access and I ended up giving it the workspace ID. This also happens with AI Agents a lot. They mess up. So make sure that you’re using the correct data. Also double check in swagger UI. I ended up actually creating the Bearer token manually to verify which thing in the chain of events was messing things up. And it’s n8n and ClickUp at the same time. ClickUp will also give you some BS about missing OAuth Tokens when in fact you were just accessing something that doesn’t exist.
I hope this helps somebody. I could get my workflow back to function by just getting the test-data right again. And don’t tell me you’re certain because it worked before 
I know for a fact that this gets messy with tons and tons of IDs you’re handling and I myself was 100% sure that my data was correct.