Just for the benefit of anyone else attempting to use Indigo on a MacBook, it isn't possible to suppress sleep unless you meet Apple's strict requirements for 'clamshell mode'. Apologies if this is discussed elsewhere (I can't find on this forum). That means, you must have attached a screen, keyboard, and mouse. 'Blank plug' screen emulators are available that may bypass the need for a screen, and wireless keyboard/mouse are technically ok (if they stay charged!).
In spite of this I personally still found clamshell mode prone to break in my setup and hence not suitable for Indigo running at a remote location. In exasperation I've upgraded to a Mac Mini. Its annoying (a) because older MacBooks are super cheap and otherwise perfect for Indigo (b) have built in UPS; and (c) they are easy to mount (when closed!) in an enclosure/cupboard...but having the screen etc integrated is super handy compared with having to connect a screen to a Mini at an awkward location.
The references to anti-sleep apps such as Amphetamine appear to be a red herring (for MacBooks with the lid closed). Amphetamine's website (corroborated on the Apple support site) provides detailed explanations of clamshell mode and how it can't be subverted by an approved app.
https://amphetamine.freshdesk.com/support/solutions/articles/43000068869-amphetamine-does-not-keep-my-mac-awakeAmphetamine does call out a non-approved kernel extension as a potentially viable workaround, but presumably that carries significant risks - any tried this approach?