Code
T0036 not-sent
A call that a page held while it had no connection was not sent within limits.callHold. The call never reached the engine, and ran nothing.
Details
A call that a page makes while its network is gone is held by the page, not failed: its view reads busy and held of the call, or calls.<id>.busy and calls.<id>.held, as true. When the connection is back - the browser says it is online, or a try after 1, 2, 4 and up to 30 seconds goes through - the held calls are sent in the order they were made. Each carries an id that the page made, so the engine runs it once, however often it is sent. A call held for callHold (two minutes where the project states no other) is failed with this code, and is never sent, so a press of long ago does not land unseen.
The fix
Press again once the connection is back. Where the visitors of the app often lose their connection for longer, raise callHold in limits of the project.