Resume a paused campaign, setting its status back to sending (2) and re-driving the sending pipeline from the stage the campaign stopped at.

Only a campaign whose status is paused (3) can be resumed. The response reports the status change, not the outcome of the pipeline recovery that follows it.

This endpoint reports business-rule failures in the response body rather than with an
error status: an unknown campaign, an automation ("series") campaign, a completed campaign and a
transition that is not allowed from the campaign's current status all return 200 with succeeded
set to 0. The message text is localized to the account language, so match on succeeded rather
than on the message.