Classification based on multiple person's 4D nifti image data in nilearn

Hey nilearn experts, I was trying to use nilearn for a classification problem. I have 4D nifti image for each of the person. The data was in [64,64,30,375] dimensions. I used mean_img to reduce the time dimension. Each data is now in [64, 64, 30] dimension. Stored those data in a list. But whenever I wanted to fit those data in an estimator (for example: SVC) for training and keep running into the following error.

Am I missing something? Is there an example to do training over multiple nifti files in a classifier that I can refer to. Thank you so much.