raise PublishXmlValidationError in validate start frame

openpype/hosts/tvpaint/plugins/publish/help/validate_start_frame.xml

@@ -0,0 +1,14 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<root>
+<error id="main">
+<title>First frame</title>
+<description>## MarkIn is not set to 0
+
+MarkIn in your scene must start from 0 fram index but MarkIn is set to {current_start_frame}.
+
+### How to repair?
+
+You can modify MarkIn manually or hit the "Repair" button on the right which will change MarkIn to 0 (does not change MarkOut).
+</description>
+</error>
+</root>

openpype/hosts/tvpaint/plugins/publish/validate_start_frame.py

@@ -1,5 +1,6 @@
 import pyblish.api
 from avalon.tvpaint import lib
+from openpype.pipeline import PublishXmlValidationError
 
 
 class RepairStartFrame(pyblish.api.Action):
@@ -24,4 +25,13 @@ class ValidateStartFrame(pyblish.api.ContextPlugin):
 
     def process(self, context):
         start_frame = lib.execute_george("tv_startframe")
-        assert int(start_frame) == 0, "Start frame has to be frame 0."
+        if start_frame == 0:
+            return
+
+        raise PublishXmlValidationError(
+            self,
+            "Start frame has to be frame 0.",
+            formatting_data={
+                "current_start_frame": start_frame
+            }
+        )