Trouble setting path to a jpg in a folder

I’m trying to set up an AppleScript that will get a path from a txt file(mockUPPath.txt) on the Desktop which in theory will allow me to attach a jpg. The name of the folder and jpg will change so I can’t hard code it. I also get the body of the email from another text file on the Desktop which I managed to get working. I can get it to build the email but not find and attach the jpg.

The text in the mockUPPath.txt file looks like this: Name_Mock-up/555.jpg.
The jpg 555.jpg is in a folder “Name_Mock-up” on the Desktop
This is what I have so far (below), anyone know where I’m going wrong?

use AppleScript version "2.4" -- Yosemite (10.10) or later
use scripting additions

set AppleScript's text item delimiters to return
set theFile to ((path to desktop as text) & "mockUPText.txt")
set theData to paragraphs of (read file theFile)

set myPath to ((path to desktop as text) & "mockUPPath.txt")
set thePath to paragraphs of (read file myPath)
set newPath to (POSIX path of (path to desktop folder)) & thePath


--Email

set theMessageSubject to "Test email"
set theRecipient to "email@test.com"
set theMessageContent to theData
set theMessageAttachment to newPath

tell application "Mail"
	activate
	set theMessage to make new outgoing message with properties {visible:true, subject:theMessageSubject, content:theMessageContent & linefeed & linefeed}
	tell theMessage
		make new to recipient at end of to recipients with properties {address:theRecipient}
		make new attachment with properties {file name:theMessageAttachment as alias} at after the last word of the last paragraph
	end tell
end tell

The first thing to try is to remove paragraphs of in both cases.

I was able to do that without any issues but I’m getting an error.
Can’t make “/Users/myName/Desktop/Name_Mock-up/555.JPG” into type alias.

The problem is you are passing a POSIX path string into the as alias conversion. as alias expects an HFS path string or a file reference object. Try making this change to convert your POSIX path string into a POSIX file reference which as alias understands:

set theMessageAttachment to newPath

to

set theMessageAttachment to newPath as POSIX file

If this works, you may be able to remove as alias to simplify things further.

It worked thank you!