Hi native-education,
Please note that I do not have an Octane Render license, which means I do not support this render engine.
Have you set the path in the Preferences to your folder with the textures?
https://help.maxon.net/c4d/2024/en-us/Default.htm#html/PREFSFILES-PREF_FILE_MAIN_GROUP.html#PREF_FILE_TEXPATHS
Paying for images, some tips:
I assume you have a good source for images, so place them into a folder to access those for each new project instead of saving them during the work. (Archiving them should be done with save with Assets.) Good textures-sellers tell you on their website at which light temperature they were shot or corrected to a specific one.
Also, they should be in Adobe RGB or a larger color space. The tiny space sRGB can't even reproduce all reflective surface colors (Points's Gamut), and only a third of the visible frequencies, AKA: colors. Converting an sRGB to a larger space doesn't bring clipped colors back.
If you spend money, find the best source. R17, as an age reference, should be checked carefully.
I have my fair share in architecture, to know that colors are a critical point. If you use HDRI, avoid ".hdr" formats at all costs (typically no color management and no information on what was used, but some save it as EXR, which doesn't improve anything.) Some offer even white-balanced HDRI images, missing the whole point while explaining it with even weirder ideas, which is sadly done to some of our Asset Browser material as well, to make the swappable while removing all the correct colors. Be picky, to keep it short.
All the best