Formula: Convert File URL in Trigger Attachments Table to File ID

You can use a Tables: Apply formulas to columns step to convert the file URL in a trigger-attachments table (generated by an email trigger) to just file ID, for reference in subsequent steps:

var prefix = "https://{{team.teamName}}.pushbot.com/v1/teams/{{team.teamName}}/files/"
var suffix = "/download"
columns["file"] = columns["file"].replace(prefix,"").replace(suffix,"")