90 minute historical bars?

Is there a way to get 90 minute bars, historically?

In the bar parameters I tried “90Min” (there’s a max of 59 mins) and “1.5Hour” - got the response “invalid timeframe: invalid timeframe format”

I’m presuming it’s not possible…

AFAIK it’s not possible. You can request bars using the “30Min” timeframe and re-sample them on the client-side.