Facebook complains that the app is not secure - facebook

Question

When I try to login via Facebook, it throws the following error;
facebook has detected app isn't using a secure connection to transfer information
But I'm pretty sure that it is secured via 'Let's encrypt'.
I have checked Web and Client OAuth login boxes and set the corresponding redirect uris on developer facebook.
On maui side, I am calling the following code piece and AppSettings.BaseUrl is correct, I have checked that;
WebAuthenticatorResult authResult = await WebAuthenticator.Default.AuthenticateAsync(
new WebAuthenticatorOptions()
{
Url = new Uri($"{AppSettings.BaseUrl}account/authentication/{scheme}"),
CallbackUrl = new Uri("tibi://"),
PrefersEphemeralWebBrowserSession = true
});
And on backend side, the following api is requested;
[HttpGet("authentication/{scheme}")]
[AllowAnonymous]
public async Task Get([FromRoute] string scheme)
{
var auth = await Request.HttpContext.AuthenticateAsync(scheme);
if (!auth.Succeeded
|| auth?.Principal == null
|| !auth.Principal.Identities.Any(id => id.IsAuthenticated)
|| string.IsNullOrEmpty(auth.Properties.GetTokenValue("access_token")))
{
// Not authenticated, challenge
await Request.HttpContext.ChallengeAsync(scheme);
}
else
{
var claims = auth.Principal.Identities.FirstOrDefault()?.Claims;
var email = string.Empty;
email = claims?.FirstOrDefault(c => c.Type == System.Security.Claims.ClaimTypes.Email)?.Value;
// Get parameters to send back to the callback
var qs = new Dictionary<string, string>
{
{ "access_token", auth.Properties.GetTokenValue("access_token") },
{ "refresh_token", auth.Properties.GetTokenValue("refresh_token") ?? string.Empty },
{ "expires_in", (auth.Properties.ExpiresUtc?.ToUnixTimeSeconds() ?? -1).ToString() },
{ "email", email }
};
// Build the result url
var url = callbackScheme + "://#" + string.Join(
"&",
qs.Where(kvp => !string.IsNullOrEmpty(kvp.Value) && kvp.Value != "-1")
.Select(kvp => $"{WebUtility.UrlEncode(kvp.Key)}={WebUtility.UrlEncode(kvp.Value)}"));
// Redirect to final url
Request.Host = HostString.FromUriComponent(AppSettingsProvider.GatewayUrl);
Request.HttpContext.Response.Redirect(url);
}
}
Challenge is invoked successfully and redirects me to the Facebook login but when I sign in, I get the error above.