I purchased an SSD upgrade kit for an iMac late 2015 27". The install went flawlessly, following the directions online. The drive is partitioned with a 121GB volume and a 1TB volume. I was able to install the OS onto the 121GB, but no matter what I do I cannot format the 1TB volume.
It is labeled CT1000MX500SSD1 Media, is uninitialized, and is an Unsupported Partition Map. Each time I try to erase I end up with "Erase process has failed" and "Wiping volume data to prevent accidental probing failed: (-69825). I have a 1TB SSD with the only usable portion containing the OS. What am I missing?