There is a related thread about Maintenance Mode (which contains the "Service is overloaded" message) response from the API, here: https://devcommunity.ringcentral.com/ringcentraldev/topics/maintenance-mode-tgdbq5wfmye11

Here is the "key" part of what Anton mentioned in the other thread...

"Usually this error code along with HTTP 503 status can be returned when traffic is switched between our data centers. It usually can happen at night time when API traffic is minimal and doesn't last longer than 10-15 seconds. In case of such error API also returns Retry-After HTTP header which indicates when client should retry the original request."

Is this what you're experiencing and does Anton's response address what you're seeing?

If not, please contact customer support for any immediate or service issues you might be experiencing.

---

Even sometimes we face this issue and it is automatically resolved after 15 to 20 seconds of time. It can happen for many reasons like maintenance as you said or even high traffic and services not accessible for that time. Whatever be the reason you cannot predict so, better you can ask the developer support team for help and create a support ticket. You need to provide your account details for them to investigate the exact reason. You can also create a support ticket regarding the same.

---