If you're upgrading to an SSD, before you even take this first step, I'd recommend putting the SSD into an external drive case, using USB and format the SSD first before trying to swap your existing hard drive or implementing a fusion drive. The external drive case will come in handy later so you can use the old drive as extra storage anyhow.

Once that SSD is internal, the Mac errors out during the formatting process. Once it was formatted externally, then installed inside the Mac again, there was no problem.