Connection error with Splunk HEC data input?

[newuser1243]

Hello,

I'm trying to create a data input as HEC to receive data from cribl.

In cribs I created a destination as Splunk HEC 

In Splunk I created a data input HEC but it keeps giving errors. 

I'm using a free cloud trial of Splunk, I managed to get the HEC uri as per the Splunk docs:

https://http-inputs-newinstance123.splunkcloud.com:8088/services/collector/event

but I still get the attached errors in cribl.

Any help ?