Registering an agent with VSTS and getting the message "Agent pool not found"

When you want to register a build agent with VSTS, you use the VSTS instance’s URL and a user’s Personal Access Token (PAT). Whilst doing this today I connected to the VSTS instance OK but got the error "Agent pool not found".when I was asked to pick the agent pool to add the new agent to.

As the user who’s PAT I was using was a Build Administrator I was a bit confused, but then I remembered to check their user access level. It was set to Stakeholder, once this was changed to Basic I was able to register the agent without use.

Also, so as to not use up a Basic license, when I did not need to, I swapped the user back to being a Stakeholder once the agent was registered. This can be done as the token used for the actual build is not the one used to register it, but one assigned at build time by VSTS.