It can be used with Unity Humanoid avatars set to the T-pose.
Additionally, the avatar must include an Animator, and the bones must be properly configured.
Additionally, the avatar must have a mesh corresponding to the torso based on the body type.
Yes, A-Pose avatars are supported.
For A-Pose avatars, please check [A Pose Avatar] next to the avatar assignment field, as shown in the image below.

When this option is enabled, the tool will automatically adjust the avatar’s arms into a T-Pose-like shape, as shown below, and then proceed with the fitting process.

If there is a significant difference in body type, especially in bust size, the transformation may look unnatural or the fitting may fail.
For stable results,