Hi @Anonymous,
Are you using PowerApps to build the Vocation request, or using Microsoft Flow?
Could you please share more details about the App (and the flow ) you mentioned here?
If you would like to grab the user name, we could take use of the user() function to get the user name of the current user, then use this as the value input under the flow (under Flow corresponding box choose Ask in PowerApps) you configured.
Then under PowerApps, specify the corresponding value as:
User().FullName&"Would apply Vocation"
For example:

Then within PowerApps, the onselect property of the button used to submit the request should be:
Sendapprovalemailwhenanewitemisadded.Run(
Office365Users.Manager(User().Email).Mail,
User().FullName&" Would Apply "&TextInput1.Text&"Days for "&TextInput2.Text)

This would have the user send the Email with the Details specified within PowerApps, then pass it into Microsoft Flow.
Regards,
Michael