Facebook Conversion API: "System users can not have duplicate names. Use another name."

I'm trying to create access tokens for a few of my pixels, but I'm unable to do so due to the error message "System users can not have duplicate names. Use another name.".

This is the error I get in the pixel settings, when I click Create access token:

Failed to create access token. System users can not have duplicate names. Use another name.

I don't know what this means in this context, or what I need to do to fix it and create my access tokens.

PS. Thread on Facebook Developer Community Forum; no responses at the time of posting here.

Only way that this error was resolved was to be made a complete Business Manager admin on the account. Once that access level was granted to me, the error disappeared, and I was able to generate access tokens.