Why are FFT numbers so high? My input numbers are close to 10, here is a sample of some:

9.259992,9.253408,9.322236,9.375503,9.406026,9.507771,9.509567,9.403034,9.397048,9.36054,9.265977,9.262985,9.216302,9.228272,9.338395,9.430565


I am using this PHP library
thinkingmik/FastFourierTransformation

My peak numbers in response are about 500. A control which was done using another tool is 1-1.5

FFT is well over my head, so I am trying to read this library to get a bit of an idea, but can't figure this out. The interesting thing is the client says the chart seems to be correct, just numerical values are wrong.
As pointed out by Dan Boschen in a comment, these number aren't really surprising. Usually the DFT is defined as

$$X[k]=\sum_{n=0}^{N-1}x[n]e^{-j2\pi kn/N}\tag{1}$$

where $x[n]$ is the input sequence and $N$ is the DFT length. So bin zero, i.e., $X[0]$, is just the average value of your input sequence multiplied by the DFT length. The maximum value of $|X[k]|$ can be as large as the maximum value of $|x[n]|$ multiplied by the DFT length.