Hi Sanjaya
If I remember correctly when I was working with the trial tenant, you don't need to update the keystore to access Gmail. But you do need to deploy user credentials for GMail as mentioned in the blog below.
Building your first iFlow - Part 4: Configuring your credentials
I'd suggest you also try to test the outbound SMTP connection first prior to deploying the iFlow. You can follow the steps mentioned in my blog below.
HCI: Testing Outbound Connections from HCI
Regarding the Checkjobs error, can you show a screenshow after you click the Details section?
Regards
Eng Swee