Install plugin into Jira without token

[Deleted user]

I install my plugin (custom slack integration) in jira but during the installation I get the answer like 

errorMessage: "invalid token",
subCode: "upm.error.invalid.token"

with path '/rest/plugins/1.0/?token=4708...', got 403.

why this can happen?

Thanks

[Former user]

Same problem here. We have 1 JIRA installation were we keep getting this error as well, whereas for other installations we do not get the error, calling the exact same methods ...