I am using this interface: https://developers.google.com/gmail/api/v1/reference/users/messages/send#examples
I was testing API request from the form on the website. It requires raw Base64 encoded string such as:
TUlNRS1WZXJzaW9uOiAxLjANClJlY2VpdmVkOiBieSAxMC4xOTQuNjguMjI3IHdpdGggSFRUUDsgV2VkLCAyNCBBdWcgMjAxNiAwMjo1OToxNyAtMDcwMCAoUERUKQ0KRGF0ZTogV2VkLCAyNCBBdWcgMjAxNiAxMTo1OToxNyArMDIwMA0KRGVsaXZlcmVkLVRvOiBrcnVub0B1bGl4dHJhdmVsLmNvbQ0KTWVzc2FnZS1JRDogPENBSzB5QmZZeEgwS1dGbng2TzNfZ3ZNRkxtVlB5RVY9NjdnQW5qRWdPaHIzSGZOTkJCUUBtYWlsLmdtYWlsLmNvbT4NClN1YmplY3Q6IFRoaXMgaXMgYSBzdWJqZWN0DQpGcm9tOiBLcnVub3NsYXYgVUxJWFRyYXZlbCA8a3J1bm9AdWxpeHRyYXZlbC5jb20-DQpUbzogS3J1bm9zbGF2IEJhbm92YWMgPGt1bm9rZGV2QGdtYWlsLmNvbT4NCkNvbnRlbnQtVHlwZTogbXVsdGlwYXJ0L2FsdGVybmF0aXZlOyBib3VuZGFyeT0wNDdkN2JhZTQ5NjRhMmQ3MzAwNTNhY2U1NWUxDQoNCi0tMDQ3ZDdiYWU0OTY0YTJkNzMwMDUzYWNlNTVlMQ0KQ29udGVudC1UeXBlOiB0ZXh0L3BsYWluOyBjaGFyc2V0PVVURi04DQoNClRoaXMgaXMgYSBib2R5DQoNCi0tMDQ3ZDdiYWU0OTY0YTJkNzMwMDUzYWNlNTVlMQ0KQ29udGVudC1UeXBlOiB0ZXh0L2h0bWw7IGNoYXJzZXQ9VVRGLTgNCg0KPGRpdiBkaXI9Imx0ciI-VGhpcyBpcyBhIGJvZHk8YnI-PC9kaXY-DQoNCi0tMDQ3ZDdiYWU0OTY0YTJkNzMwMDUzYWNlNTVlMS0t
How do I instead use basic parameters (such as subject, sender, reciver, message body) to send mail?