How to Use Decals In Wildcat PBR Modeling?

Hello. I'm making a PBR model for CGTrader Wildcat. Some parts of the model I made were asked to be made as decals. So I added a UDIM to the UV set of the model and put the UV of those sections in the new section. Then I created a separate PBR texture set for that section in Substance Painter and uploaded the model with two Texture sets. I named the Decal Texture M_1_2.

However, I got a revision like this: "Marked parts should be used as decals (logos, side vents). Check Technical Requirments sheet for detailed information"

Do you have any idea what I'm doing wrong? How to add a decal?

This subject is not explained clearly enough in the Technical Requirments Sheet.