Getting We couldn't complete your request. Resolve the following errors and try again. One or more inputs in action (Apex:Prompt_Program_Recommendation_Invocable) don’t match the required object type. Update your input types and try again. Sender error

I was able to progress on this using below steps :  

1. Under setup go to "Einstein for Sales"  (This is as of today. not sure when they change the name again) 

2.  Turn on " Turn on Sales Emails " and wait for some time. It does something in the backend. 

3. Now go ahead and create the Prompt Template. This time you should see "Sales Email" as the Template type. 

4. Once configured, these will show up and it should resolve the issue :