Use Keystone to authenticate - Issues with REST API query - help!

I am new to OpenStack and trying to get an authentication token. I get errors and maybe someone can provide me with some guidance. I have tried with Postman client and curl script.

Base url: http://xxx.xxx.xxx.xxx:5000/v3/auth/tokens

I have a basic user: user123
password: pass123
Domain: I assume default? Is that correct? I do not think domain-ids have been created
methods: password (I assume)
user123 is part of 2 separate Tenants

I have tried the following:

curl -i --insecure http://xxx.xxx.xxx.xxx:5000/v3/auth/tokens -X POST -H "Content-Type:application/json" -d "{"auth": {"scope": {"project": {"domain": {"id": "default"},"name": "user123"}},"identity": {"password": {"user": {"domain": {"id": "default"},"password": "pass123","name": "user123"}},"methods": ["password"]}}}"

I get errors:

"Expecting to find application/json in Content-Type header - the server could not comply with the request since it is either malformed or otherwise incorrect..."

Please help with the format above! Thank you in advance!!

KP