You can view the installation guide from here.

Optimum Realism is currently supported only on Minecraft Java Edition and has partial support on Minecraft Bedrock Edition(RTX)

Optimum Realism 128x is free, 256x and above versions of Optimum Realism which have a much better look and have better quality are patron-exclusive only. You can find the link to the Patreon page as well as the demo version here.

You should be fine with something like a GTX 1050 or above and a decent processor, the amount of ram required depends on whether you downloaded the 128x,512x or 1024x version of Optimum Realism. 8GB of ram should be fine for 128x and 512x. 16GB of ram is recommended to run the 1024x version of Optimum Realism to have sustainable fps.

Creating such textures, is a very long journey, and making a good texture pack that is an effect of constant feedback from the people who play with it and applying that feedback in the workflow to create a product that's worth your time takes a long time (18 months as of writing this) and to make such textures a combination of programmes are required which cost quite a lot monthly. Another important thing to note is that I do not get everything of what you pay. Patreon and Gumroad both charge their platform fees, as well as taxes and forex charges.

If you purchase the Patreon membership, you could directly message support, otherwise, you could also just report it on our discord server.

Optimum Realism has to be played with a shader, it is recommended, but not necessary to play it with either Kappa, Kappa PT or SEUS PTGI HRR 2.1, depending upon your taste. Make sure to download the variant likewise.

Optimum Realism is currently unavailable to play on any mobile device on Minecraft Bedrock Edition. However it can be played by using mods like Pojav Launcher that run the Java Edition of Minecraft

Depending on which resolution you want it for, the membership tiers range from $3 to $15.

Optimum Realism is created with almost a year of work. The textures are created in many ways, mainly by using a combination of dedicated high-end softwares.

Whether you're eligible for a refund, depends on the site you purchased the membership for Optimum Realism from, and whether the reason stated is convincible.