@Caraline0
I made a point back at the start of this thread in 2018 that there is nothing wrong with either the app or the wifi, you just need to understand the way Wifi works.
You will always receive an sms message because that is generated through your cellular network as a cellular notification and does not use the app! But, a number of factors govern whether you can respond to that sms, the main one being you need to respond through the mobile app! You can't respond through the notification.
1/......If you have Wifi turned on on your phone and you are in a public Wifi area and not logged into that wifi signal such as, (sometimes you will walk into the local Laundromat and on entering you will get an sms prompt to long into that laundromats free wifi service) if you don't, and you don't turn your wifi off on your phone you will not be able to respond! The strongest wifi signal will block your cellular phone from accessing the mobile app....that little 'wheel of death' will just keep spinning!
In that situation turn your phone wifi off and you will be able to respond through the app message stream via your phones cellular signal.
2/......If you run your phones battery charge down below a certain point the phone goes into 'survival mode' and deactivates unnecessary features and most commonly your data access will be restricted......you will be able to receive messages, but not respond to them!
If you are not in a 'personal' phone recognised wifi area (wifi range you are linked to) and you cannot respond through the app it is possibly because your Mobile data has turned off! In this situation go to your phones 'setting' > 'Sim Card & mobile data' > 'Mobile data' and make sure this is activated as per this screenshot.....

Caraline, you can always respond through the mobile app, you don't need to be in your home wifi range, it is best when away from home to go into your phones setting and turn your wifi off and make sure Mobile data is turned on.....you will never get caught then....but remember to turn your wifi on again when you return home!
I hope this makes sense, but trust me it works!
Cheers.........Rob
@Paul8494 @Helen3 @Eddie327