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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.