Cloud connection failure. token Failed (status code 503)

Troubleshooting
1

I’m suddenly getting this showstopper when my cloud SDK app on iPhone tries to connect to Particle cloud in order to read data from Asset Tracker Electron.

loginWithUser https://api.particle.io/oauth/token Failed (status code 503): {
error = “server_error”;
“error_description” = “server_error”;

ANOTHER OF MY APPS, THAT USED TO WORK, NOW REPORTS THIS:
getDevices https://api.particle.io/v1/devices Failed (status code 400): {
error = “invalid_request”;
“error_description” = “The access token was not found”;

How do I correct my access token?

App is running on iPhone with iOS10.

I can use iOS Particle app to logout and log back in, and to read the same data from cloud that my SDK app can no longer read.