Offline error, error 905 / 503 no access to my cloud from outside

Good morning,

i have a my cloud 4 TB drive.
As WLAN I am using Google Wifi connected to AVM Fritzbox
MY ISP is Kabel Deutschland / Vodafone

I can access my cloud drive as long as I am within my own WLAN area.
But I don’t get any access within another WLAN area or when using mobile network

On my iphone I receive error “Drive offline”
On my Android “Error 503”)

Do I have to adjust some seetings in Fritzbox and/or Google Wifi to gain access from outside my home?

Thanks for any hints,
Jens

Did you set up everything in the Dashboard and give each device access? See example image below, click on, tap or activate image to enlarge it and see complete image.