hey @Balram I don’t think there is any REST API v3 operation specifically related to the VM to power it on, but you can do so using PUT /vms/UUID v3 opeartion
To update a VM's specs, we need to send an HTTP PUT request to the Prism Central IP. The request body should contain all current specs of the VM. The easiest way to get a VM's specs is to send a GET request to /vms/uuid
Now in the below output of GET operation, Scroll down to the Response Body text box. Find the spec key and copy starting from "spec" down to the last closing curly brace "}". Paste it to a text editor.
For eg-
{
"spec": {
"cluster_reference": {
"kind": "cluster",
"name": "Prolix",
"uuid": "00052c80-729d-8705-0000-0000000051fa"
},
"description": "v3api_vm",
"resources": {
"vnuma_config": {
"num_vnuma_nodes": 0
},
"nic_list": [
{
"ip_endpoint_list": [],
"nic_type": "NORMAL_NIC",
"subnet_reference": {
"kind": "subnet",
"name": "vlan25",
"uuid": "565784d2-7a68-4a16-a1bd-92473760f607"
},
"uuid": "4bff96c1-386e-40bb-bc5b-1dc8a85952af",
"mac_address": "50:6b:8d:b4:76:12"
}
],
"num_vcpus_per_socket": 2,
"num_sockets": 1,
"gpu_list": [],
"memory_size_mib": 4096,
"power_state": "OFF",
"hardware_clock_timezone": "UTC",
"power_state_mechanism": {
"mechanism": "HARD"
},
"vga_console_enabled": true,
"disk_list": [
{
"device_properties": {
"disk_address": {
"device_index": 1,
"adapter_type": "SCSI"
},
"device_type": "DISK"
},
"uuid": "948915d8-1f99-46f3-a249-39151f3f518a",
"disk_size_bytes": 26484932608,
"disk_size_mib": 25258
}
]
},
"name": "nuran_v3api"
},
"api_version": "3.1",
"metadata": {
"last_update_time": "2018-11-03T00:26:41Z",
"kind": "vm",
"uuid": "042dada0-2f55-4001-a6f1-70d7b88e323c",
"project_reference": {
"kind": "project",
"name": "default",
"uuid": "f86d420a-f601-4ca9-9135-082bc38554c6"
},
"spec_version": 1,
"creation_time": "2018-11-02T20:42:52Z",
"owner_reference": {
"kind": "user",
"uuid": "00000000-0000-0000-0000-000000000000",
"name": "admin"
},
"categories": {}
}
}
Now, you can update any parameter in the above, you power on a VM, update its configuration, add new disk etc.
or another way is by using the Powershell scripts:
Here is a list of entities which you can manage using PowerShell CMDlets: https://portal.nutanix.com/page/documents/details?targetId=API_Ref-Acr_v4_6%3APowerShell_Cmdlets_Reference
Also, this PowerShell CMDlets cheatsheet would be useful:

You can check out the Powershell commands under Acropolis Task administration(2nd column in the above screenshot) to create a new VM, Power it on etc,