Import certificate API for azure key vault

i am trying to import a certificate through REST API to azure key vault, via Postman. For that purpose, i have generated the bearer token via, "https://login.microsoftonline.com/tenant_ID/oauth2/token." I am having two headers, The authorization and the content-type. My request body would look something like
{
"value": "",
"policy": {
"key_props": {
"exportable": true,
"kty": "RSA",
"key_size": 2048,
"reuse_key": false
},
"secret_props": {
"contentType": "application/x-pkcs12"
}
}
}

I am not understanding what i need to pass inside the "value" parameter. When i am passing the base64 encoded data of certificate, it is throwing an error saying,"No certificate with private key found in the specified X.509 certificate content. Please specify X.509 certificate content with only one certificate containing private key."
And when i am passing the whole contents of my cert as such, I am getting the error,"The specified PKCS#12 X.509 certificate content can not be read. Please check if certificate is in valid PKCS#12 format."
So can you see this whether I am doing something wrong from my side. Please do address this with priority since our security is being compromised due to this blockage. Thanks in advance!