Getting logs into splunk in a different index other than main?

[icsy7867]

I am working with our splunk admin, but we cannot get the logs to appear anywhere but "main". We are using an HEC token. Logs make it to splunk (Using splunk cloud) main index without issue. But if we set the token to go to a specific index, or try to change the index we see things like:

parsing_err="invalid_index='main'"

I also tried to edit the metadata csv file using something like:

some_label,index,my_custom_index

But no luck. I am new to splunk, and I apologize if this is a dumb post, but I am not sure where to start. Any ideas?