Say the ID the player sent was something like 12345. You would only have to do rbxassetid:// No complicated URLs or anything. EmbatTheHybrid’s solution also works too.
My solution doesn’t turn it into a image. Ignore mine lol.
Issue is that your method wont convert the decal id into an image id, which is probably what was happening to @OP, the url I used does that for you, so even if you give a decal id, it’ll still turn it into an Image ID