I had the same problem, however, I'm using RestSharp for HTTP requests.
My problem is that I was passing an image in the body in base64, but I should pass that image in binary.
You're probably passing the file in the wrong format. You can try using file.create to create the file in the correct format before submitting .
I do not know if it helps, but this is my code:
[HttpPost]
public string PostImage(){
var restclient = new RestClient(BaseUrl);
RestRequest request = new RestRequest("/upload/drive/v3/files?uploadType=media") {Method = Method.POST};
string imageBase64 = "/9j/4AAQSkZJRgABAQAAAQABAAD/2wCEAAkGBwgHBgkIBwgKCgkLDRYPDQwMDRsUFRAWIB0iIiAdHx8kKDQsJCYxJx8fLT0tMTU3Ojo6Iys/RD84QzQ5OjcBCgoKDQwNGg8PGjclHyU3Nzc3Nzc3Nzc3Nzc3Nzc3Nzc3Nzc3Nzc3Nzc3Nzc3Nzc3Nzc3Nzc3Nzc3Nzc3Nzc3N//AABEIAIUAyAMBEQACEQEDEQH/xAAcAAABBQEBAQAAAAAAAAAAAAAAAQIDBAUGBwj/xAA6EAABAwIDBgMFBgYDAQAAAAABAAIDBBEFITESE0FRYXEGIpEUMkJSgSMzYqGx0QdDgpLB4TVTchX/xAAaAQEAAwEBAQAAAAAAAAAAAAAAAQIDBQQG/8QAMREAAgIBAwMDAgMIAwAAAAAAAAECAxEEEjETIUEFMlEiYRRCkSMzUoGhsdHhNHHx/9oADAMBAAIRAxEAPwD3FACAEAhNkA3eM29jbbt2vs3zsoyuAOupAqAEAIAQAgBACAEAIAQAgBACAEAIAQAgBACAEAIAQHmuNfxbw6mdUx4dRzVIieWNqLjdvIyJGdyL8eKxnbjsuT1Vafd3lweTYx4sbisrq+eB7nSEh0r7B3qNOnJYKpuXd9z2SuShiKwj1Dwx4nw6WppW4dLNE6Vzd5Bsm0Y47V8lza650XdSUsL+hWVfUi8dz1FrgRdpuOi7yaayjltY5FUgVACAEAIAQAgBACAEAIAQAgBACAEAIAQAgBACA+WMQpGYfUzYdUl0LaV7omGUZua0kA+i8UstvB168OKJcOo4a2WKjpm3iik3jnvGVwf04WWVk3FOTNopP6T0ajw+Cima+NgjEoIDguDZfOyDT8HpUYo3KXFp6c7hz3MeORycOYVY6i2lfRLseedMJvg0I8YqOEzvqVovUblxIyelh8FuHHKgZOLHjsvRX6tcvdhmMtHHwX4MbiebSsc3qMwuhV6tXLtNYPNLSyXBoQ1MU33cjXdL5roV6iqz2SyeeUJR5RMtioIAQAgBACAEAIAQAgBACAEAIAQAgBAeK/xHwanxfGhK8ENjndtluV22zHqFw43OF1qXydiFalXHPhGRhrGU+J7IY1jZQAABYDkpt71myWGdjFEKuhdBtBr2+aN54EaLjb1XZ34Zq35K1PWMqmmmrWbM0brFpNnNPQq1lU6frqeUThM04qcAACZ3dwzXkzGfddiHLHKJN1PHYtAcPw5qHBruhvhIfHUcDe6je1yVdZZZOrK15MZQL1PidRFk2Qub8rs17qvU76+Hkwnp4S8GjBjLTlPER1bmunV61F/vI4PNLStcMux4hSyaSgf+sl0Ia/Tz/N+vYxdM14JmzRu917T2K9KthLhme1/A8EHRWyiAupAIAugAuaNSAo3JDDAOB0IKKSfAwwupAXQCoAQAgBAVcRq20VHLUPt5BkOZ4LDU3qip2PwaVVuyaijyrFyZWukc67r3J5kr5ume6XfydvG1YOfmLWP27jJtwV0EsrAZ2eHwyFokAIBANlxrI7m0XTwT1eHU1e5rpBu52izZG5ZcjzCtVa61tfBTLi8kFqmjLWT+ZugeNCsLaYvvE3i4zXYtwzg6HNYqbj2ZnKD8k5cyUfagO68Qrb0+zM+8eBjqZ4zhdtjiDqqurPeJZWL8xEJSw2NwRzWWJRL7U+CRtQeao7JIzdZIKm+pRXMr0x2+B4qeqV2D2zn5leN0/kjYPFS8fG5bLUWLyV6aFNZIB9471V/xdq/MOkn4GGtedXOP1Vfxc3yy3SQ11TfUrN6hkqsYZwq9b7k7Bpq5Izdkj29nFFqbE/pb/Ut0ovlFSHxXiVH4soqWd28wuZgjffZ2myONmkHW3Puvq/SdROyn9o8vJ4NXQovMUeijRdc8AqAEAIDnMdf7bLuAfsozc24uXz/qM+vPYn2X9/8AR0dKumt3lnN1uFxPa/XMWXMblU+zPepbuTk6/D2xzNa4eRxsujTfvjnyS4ncxEBthwOS5tc/pyUku4Scx7ymXdExHsex7Cx4DgciCFRPHJSUWnlGbV0z6S8sV3Q8ebVEq4yPTXap9pciwVYyDl5pVSjwTKousnGVlVTweeUCVzmSi0rQR+a06ifZoot0e6ZXdSDWKT6OUOMXwzVXfKGmlnA0a7sVR0PwSrIMaYphrE/6BUenl8E5g+GJaT/rf/aVXpteB9PyOG+Okcn9pU7LPgj6fkeIah38p31VlVY/BG6C8i+zTH3nMb9bqypl5ZHUiOFMB78p+gU9KvyyHY/CF3EI+Y93Jsq+CN8hRBAdR+alQgRvmUqvC8EfUMqqqmifNEQ5j3EktINxbrde/T6qdXaLIlCVnKLPhPxlPX+JJ8Jrjk9hkpy5lnC2oNsuoX1NFvUjlnMvqUH2O9XoPOCAhqpNzTySD4WkrK6eytyLQjukkcq59ma3XyykddRKkrrleeyXc3ijBxyn3lO4MyeR5TyPBX0dm2Zo+DQoKts8TJWnJ7Q63JYNOqTi/BEllFouvxV9xVITatmCqSfwTjJaglDhb1UxsXkxlHBn12HFhMtILt1MY4dv2Wrxg9FV/wCWZUhmIzaVhOtPk9EoJlyOrys5YOtrgwlT8E7Khp4rJyceUZOtkrZRwJUq37mbiSNlWsbXjko4jzMeDj6rTq/cbRu8cfiNk6n3J2oa6QNGbh6qrn9wo58ED6uFurgT0Ue7hGqpk/BWkxBvwNv3V1S33ZtHT/LKzq2VxysB0WnRWDTpQQ0zSO1cVCqihiK4InXdqtFiPBGfBueE8ABxRmKyR7Lo2lrXfNdd70uNrTlL2+Dka6yDe1cndLsHOBAU8X/4+bt/leTXf8eRtp/3iOScciF8pux2OwkQOuVjOXc0KlXHtxFUpntmW8GJhdR7JVS4fIciTLD2JzH0P6hdPU1dWKsX8ysX4NyOXJc5pouSNeLqNwaHA7OipIjBcgqBo7Iq9d2O0jCVb5RHV4fFVXfE7dy87ZHuvQseCa75Q7Pgy5opqV2zMy3JwzBUNZPdCcbFmI0PHBVwWwOEjho4qjhF8oq4pj9+/wCb1VHTAr00G/f8wRUxI6aGmZ/zFXVUfgtsRE5xOpK0jHHBbjgiLraLVINiHNTgqOaFVsq2TsjJsAsZTKs6LA8C3pE1SLMB0PFdnQemueLLl2+Dm6rWL2QOtYxrGhrRYDIAL6BHKHKQCAr1zN5SStAudk2WGpjvpkvsXrltmmcbLkvjLHhncRAVhJlsDHC+SybLGHjeHPlaJaYtbURO24nHS/I9DoupotUvbLhhxzwJhmICqhuGljgdl8bveYeIK01Gm2MJmkx99F4ZRLkrX81m0B97rNoholildGcjkoUnHgpKKkXGVMb27MgB6ELeN6fZmDra7ohlwuknF4iYnfh09F6IyUuGXjqbIc9ypJg9Uz7t8cg9CrbTeOsrfuWCu+jrI/egf/SLquEaq6qXDIXCRps6N47tKYRonF+Rm0eRTCJwIS46NJ+issEDDtX913orJogGi7w0uFzoCcyrN9smbwa9BhlTVEbqM2PxHRVq012of7OPb58Hntvrr9zOowvAIqbZkn87+XBd3Sel10vdPvI5V+snZ2j2RuNFhYaLqnjFQAgBAIUBx+LU/s9VJGB5b3b2K+P9Qp6VridnT2b4JmcuVk9ItlVgY5oKopbXknJgYrhksUxraIHefzIx8Y/ddrSayM49OwnHlDaGvbM0WOfda3adxJTNNkgdoV4ZQZYla/qspRBIHhZODK4H3BVHFkYHMkcw3Y4hFuXBDinyTtrZW62PdaRusRR0xHCvePgH0Wn4iXwV6CYv/wBF/BqdeXwPw6GOr5fwqOrJk9CI32+XoE6kiehAa6vmdq4eiOUnySqIIqzOpZaiOonpYJJ4zdkroxtNPQrWq2+HsYlp4SLjfEdRTQhkRyGnFdOv1LVpY7GD0NWe5Vq/4jT4U6GSsonT0xfaV8Vg5g5gcV1dJq7LMqw8t+kjHvE9FgmZUQsmicHRvaHNcDkQV0jnvsSIAQAgBAZHiCk30G+YPNHr1C5Xqmm6te9cr+x69JbtltfDOUeNk5L5Ca2s66AFUZIEXVJIqNLcrWVFJplsmRieC715npCGTHUH3X9+R6rq6X1FRW2zgnOTNhrZYJDDUNdG8atcM/8AfddJ1QsW6DyiU/k0IqsOAIddeWVDRYssmBzWDrYJBL1WbrA7eqvTAu96qOmQG9TpAN6mwCbxTsAhkUqAGmRXVYyRudtZK6WAyNzNpaKWCuCtUYU7ER7O2Mvc/Jo5Femi2W9KHJlYo7cy4PVsHpBQYZS0gNxDE1l+wX1COC3kuKSAQAgBAI5oc0hwuCjBx2MUTqSoLQPs3ZtP+F8h6lo+hZ2X0vj/AAdnTXdSHfkzNCuPhnrHNcoIY5UcSoiyaBFVUdPWM2J4w5vC+o7LanU2UvMGMsxpvD88Xmopw4D4Zcj6hdar1WEli2P81/gspEQjrqf76lksOLfMPyXoVuns9kl/YumhzKi+RuO4sjrJRIJ+qp0y2B296hRsGBRIeahxGBwe7RRhENAXuU7UVAbR1JTsVHtaSqOSBMyIHusZWElyloXzyBsbddTyW+l0l+qf09l8mF19dS78nVYPhUNGA8jblOrivqNLoq9MsR5+fJyLtRO55fBtNGS9ZgKgBACAEAICriFHHWU7o368DyKxvohdW4T4L12OuW5HFVdNJTTGKVtnD0K+L1Wknp7Nk/8A07lVsbY5RBdeRrJqK11lRxaIaHhwVH9yMAqbRgLkaJgYF2uKrhkYAuB4XRJrgnDEuPlCt9XyO41xYAfs2+i0ipfxE4fyQmVrdI2jsFuqpPmTL4+5z3ip9e9sE9BLI0w7RLGNvckakceX1XY9OhUsxn5+Tz3qa7wLuFyGqoKadzTvJImucNmxvxyWV0GrHFLz/wBmkbE4KT7GhHTSvOTD6KY6TUz4gykr6o8yLsOGTvObLd8l6q/R75e9pf1PPLX1L29zSpsHtYyuHYBdCj0iivvL6meSzW2S9vY2KWBkQ2WNsF1UsLCPHk0IhZATDRAKgBACAEAIAQFDFMOir4rOFnj3XDgvPqNPXqIbJo0qtlXLMTi62lmo5THM2x4Hgey+S1egt00vq7r5OzTfG1duSDaXjwbjmvVHAD9pZusBtKNhGAumwBtAIoNkjHSALSNIwROmvkt41YLELnDhqt1FkixRue8C13HQLaqieolsrRlbdCqOZHUYfh7ImXLBtHVfWU1RpioxODZZKbyy+2BrdAAtTMkbGgJGMQFiONAWGCyAegBACAEAIAQAgBAVK6hhrIiyZlwqygpLbLglNxeUcbimD1NDd8bXTQ9PeH7rhar0fDcqP0OlTrVxZ+pltkBzByXFnU4vbJYZ74yUu6Hh6z2Fhd51TYBDKp2AY6Q2V1WgRF7itFFEgGucjaROSSKMvkEcTduQ8OXUrbT6WzVPC4+TC7URqXfk6XCcJENnyeaQ6lfU0aeGnhsgv9nEstlZLMjabFbQLYzHiK6AkbEgJWxhAStaAgHIAQAgBACAEAIAQAgBAMfG14sQgMTEvDlLVkuDNiT52GxWdlMLViayXhZKHtZz9X4ar4M4JWSjk8WPqFzbPSapextHshrpL3LJmS0mIQ3EtFJ3YQ7/AH+S8c/Sblw0z0R11b5IDIWe/FK3vGV55en6hflNVqqn+Ybvmng8/wBBUfg9R/Cy3Xr/AIkSxMmlNoaaZ/Ztv1WkPTdRJ8YM5ayqPk06PAa+ozm2YWHgDdy99PpMI97Xn7Hls17faCwdNhuCw0bfI3Pi46ldaMYxWIrCPA5NvLNQRADJWIHCNAODEA4NQC2CAVACAEAIAQAgBACAEAIAQAgBAIQCgI3QxnVqAidRQO1YEA32Cn+QICRlLE3RgQEzWNboEAtkAWQCoAQAgBACAEAIAQAgP//Z";
byte[] bytes = Convert.FromBase64String(imageBase64);
request.AddHeader("Content-Type", "image/jpeg");
request.AddHeader("Content-Length", "5951");
request.AddHeader("Authorization", "Bearer " + Authenticantion());
request.AddParameter("application/json", bytes, ParameterType.RequestBody);
var tResponse = restclient.Execute(request);
var responseJson = tResponse.Content;
return responseJson;
}