Zoho Flow has a major major deficiency:

there is no support for connections in the invokeURL method for deluge.

This severely limits the connection capabilities we have: for example, no APIs that use OAuth2 can be utilized in custom connections (which is practically all APIs these days), meaning that we cannot create custom widgets which expand the functionality of Zoho Flow ourselves.

For all of my custom widgets I've had to use the Zoho CRM REST API within Zoho Flow, because CRM has custom functions that do support connections with the invoke URL method.

How ridiculous? Why should we have to connect to another Zoho service which has support for these custom connections when the whole purpose of Flow is to have all the connections in one place?

This is also mentioned nowhere in the documentation.  It simply mentions that connection "someConnection" doesn't exist when trying to reference one (see the attached file.) Had to call multiple times until one team member finally revealed to me that its not supported. I said to update the documentation, but this has not been done. 

This deficiency must be fixed ASAP: Flow would be infinitely more powerful with this one small thing: support for connections in the invokeURL method in Flow. And without it, you are leaving tons of marketing potential and throwing a lot of peoples time, and your own money, down the drain. Flow would be so much more competitive if it were for this one feature!