client terminated coaching out of the blue

Hi Coaches,

I am honestly so stumped and confused. I signed a client around 3 weeks ago. She and I were doing some great work, and she was making some amazing progress.
Every week she was emailing me that everything was going well, and our coaching was changing her life.

Today, I get an email out of the blue before our coaching call (which she cancelled) saying “Hi, this is not working for me. Please send me the invoice so I can pay for the rest of the package that I owe you. Will explain more when I have more time.”

To be honest with you I am so stumped. I feel this pit of anxiety. My mind keeps spiraling into why? I did not see this coming? Was it something that I did?
I have never had to deal with something like this happening. To be honest, I am feeling both overwhelmed and confused. I feel like I have failed as a coach, but don’t even know why.

Please can you help coach me on how to best respond as I am feeling totally stumped