Error executing Calabash iOS tests Xamarin Test Cloud

I've various tests written in Calabash using Ruby. I've tried the tests locally on the simulator and on a physical device and there wasn't any issues but, when I try to execute them on the Xamarin Test Cloud it throws an error relative to the Calabash launcher. I've changed the 01_launch.rb file several times and the error persists. This is the log file:

{"type":"install","last_exception":{"class":"XTCOperationalError","message":"500\n{\"message\":\"undefined method `strip' for nil:NilClass\",\"app_id\”:\”XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX\"}","backtrace":null}} (XTCOperationalError)
./xtc-sandbox-runtime-lib/xtc/formatter/patches/calabash_common_patch.rb:64:in `raise_operational_error'
./xtc-sandbox-runtime-lib/xtc/formatter/patches/calabash_ios_patch.rb:223:in `xtc_install_app'
./xtc-sandbox-runtime-lib/xtc/formatter/patches/calabash_ios_patch.rb:129:in `relaunch'
./features/support/01_launch.rb:98:in `launch'
./features/support/01_launch.rb:340:in `Before'

I've been searching about this issue but I don't find anything related. I'm trying to test the platform in order to use it in a CI environment for a large iOS and Android app. Any help would be welcome. Thanks. P.S: The app_id is omitted, in the tests the real app_id is setted correctly.