Getting error: main.js: error: argument --app: expected" while play Appium server

Launching Appium server with command: C:\Program Files\Appium\node.exe lib\server\main.js --address 127.0.0.1 --port 4723 --app --platform-name Android --platform-version 20 --automation-name Appium --log-no-color
usage: main.js [-h] [-v] [–shell]
[–localizable-strings-dir LOCALIZABLESTRINGSDIR] [–app APP]
[–ipa IPA] [-U UDID] [-a ADDRESS] [-p PORT]
[-ca CALLBACKADDRESS] [-cp CALLBACKPORT] [-bp BOOTSTRAPPORT]
[-k] [-r BACKENDRETRIES] [–session-override] [–full-reset]
[–no-reset] [-l] [-lt LAUNCHTIMEOUT] [-g LOG]
[–log-level {info,info:debug,info:info,info:warn,info:error,warn,warn:debug,warn:info,warn:warn,warn:error,error,error:debug,error:info,error:warn,error:error,debug,debug:debug,debug:info,debug:warn,debug:error}]
[–log-timestamp] [–local-timezone] [–log-no-colors]
[-G WEBHOOK] [–native-instruments-lib]
[–app-pkg ANDROIDPACKAGE] [–app-activity ANDROIDACTIVITY]
[–app-wait-package ANDROIDWAITPACKAGE]
[–app-wait-activity ANDROIDWAITACTIVITY]
[–android-coverage ANDROIDCOVERAGE] [–avd AVD]
[–avd-args AVDARGS]
[–device-ready-timeout ANDROIDDEVICEREADYTIMEOUT] [–safari]
[–device-name DEVICENAME] [–platform-name PLATFORMNAME]
[–platform-version PLATFORMVERSION]
[–automation-name AUTOMATIONNAME] [–browser-name BROWSERNAME]
[–default-device] [–force-iphone] [–force-ipad]
[–language LANGUAGE] [–locale LOCALE]
[–calendar-format CALENDARFORMAT] [–orientation ORIENTATION]
[–tracetemplate AUTOMATIONTRACETEMPLATEPATH]
[–instruments INSTRUMENTSPATH] [–show-sim-log]
[–show-ios-log] [–nodeconfig NODECONFIG] [-ra ROBOTADDRESS]
[-rp ROBOTPORT] [–selendroid-port SELENDROIDPORT]
[–chromedriver-port CHROMEDRIVERPORT]
[–chromedriver-executable CHROMEDRIVEREXECUTABLE]
[–use-keystore] [–keystore-path KEYSTOREPATH]
[–keystore-password KEYSTOREPASSWORD] [–key-alias KEYALIAS]
[–key-password KEYPASSWORD] [–show-config] [–no-perms-check]
[–command-timeout DEFAULTCOMMANDTIMEOUT] [–keep-keychains]
[–strict-caps] [–isolate-sim-device] [–tmp TMPDIR]
[–trace-dir TRACEDIR] [–intent-action INTENTACTION]
[–intent-category INTENTCATEGORY] [–intent-flags INTENTFLAGS]
[–intent-args OPTIONALINTENTARGUMENTS]
[–dont-stop-app-on-reset] [–debug-log-spacing]
[–suppress-adb-kill-server] [–async-trace]

Appium server process ended

could you post code used for launching app.

I’m quoting 3 parameters from your log. One of these things is not like the others. You have supplied arguments to both --port and --platform-name. Why not supply and argument to --app? The error here is exactly right.