Ok Lino, scusa. forse non avevo capito bene come funziona la cosa e probabilmente la spiegazione che hai dato non é molto chiara. Forse un tema per un tuo prossimo video?
Sorry Lino, apologies. Perhaps I didn't understand how it works and the explanation was a bit confusing.
I got it to work, and I'm posting the solution here for future frustrated users.
Basically there are several steps that need to be taken in order to get UDIMs to properly work in Octane for Blender:
1. Use the TextureTile node and not just the plain Texture node.
2. Replace the last 4 digits in the UDIM file name to "1%i". So for instance, let's say your file name is the following: SPACESHIP_BASECOLOR_1001.exr in order for Octane to recognize it you have to change it to SPACESHIP_BASECOLOR_1%i.exr (at least this is what is working for me)
3. Now you need to change the number or rows in the node Grid Size (X) and (Y) to 10 and 10 (the second number should be higher if you have more than 100 UDIM tiles to match your UDIM set.
4. Now you need to change the Start value in the Node parameter to 1 because UDIMs start at 1001
5. Double check that your Digits is set to 3 because Octane disregards the first digit so it's only looking at 001, 002, 003 etc.
That should do it, but boy is it more convoluted than it needs to be. It's little things like these that keeps Octane from being more widely adopted IMHO, because otherwise as a render engine it's excellent.
As I said, Lino please consider doing a tutorial on this as one of your next videos. UDIMs are an important part of many people's workflows and I think it's critical that OTOY does as much as possible to make it as clear as possible how to properly use them in Blender. Renaming the files manually like you did is not a solution unless we're talking about a very limited number of tiles.
In the meantime, I will point to this video that ultimately was what got me to the solution. All the other information available both on this forum and other places is either incorrect, outdated, or uses the unworkable renaming solution.
https://youtu.be/vnYznjQXd8E