The SEEED Wiki for the E10-1 (bridge) provided reference for batteries and LoRa card but not the M.2 SATA II SSD.
I had no idea there were several kinds of M.2 SSDs. Two common ones are, SATA, NVME. I purchased the NVME and it did not work. Then I tried to find SATA II no luck. After much research I discovered that SATA III will work on SATA II just not up to speed. Then there are the B-Key, M-Key and B+M-Key. That is how I latched on the NVME, it had a B-Key! Again, after research, I discovered that a B+M-Key would work in a B-Key slot. So I gambled again, since I did not receive any help and purchased the following:
Reference for the M.2 SSD: TEAMGROUP MS30 512GB with SLC Cache 3D NAND TLC M.2 2280 SATA III 6Gb/s Internal Solid State Drive SSD (Read/Write Speed up to 530/430 MB/s) Compatible with Laptop & PC Desktop TM8PS7512G0C101
I also discovered that the E10-1 does not receive any power from the reTerminal! That caused some grief. After adding 12V power I could now see the M.2 SATA SSD! It is now formatted and mounted!
If there are any others who is struggling with adding M.2 SSD to their E10-1, I hope this helps reduce the frustration.