Start a form A/B test by ID. Launches the A/B setup so its variants begin serving to visitors according to
their weights, moving the setup to enabled status.
Starting a form A/B setup that has already been started returns a conflict.

An optional auto-close policy can be supplied in the request body. endsAt closes the test at a fixed
instant and must be in the future. stopOnSignificance closes the test as soon as one variant is a
statistically significant winner; on its own it is subject to a seven-day minimum runtime. Supply at least
one of the two, or omit autoClose entirely for a test that never closes automatically. The policy cannot
be changed after the test has started.

Scopes:
forms.write

Rate Limiting:
This endpoint is rate limited to 400 requests per minute.