I have the same problem:
”Error while signing in. (-1)
Check username and password or try again later.”...still - I have an active user on opensubtitles.org
A new Formuler Z10 Pro Max.
Through Formuler support I got a solution, and this worked for me (it is referred to settings on the home menu of the Formuler box):
Please try to clear the MYTVOnline2 cache in Settings > Apps > MYTVOnline2.
1+2 Great
4. If paired, white led should flash and use as BT RCU ( No IR SIgnal) changing to IR Modus brings you to IR.
It is flashing orange (or red) when I switch between TV and STB, but it functions as a BT remote. The Formuler is on the other side of a wall, so it is certainly not in IR modus. Since everything thing is working as it should, I guess I just ignore the color of the blinking light when changing modes 
1. Go to Market, choose Formuler Remote app and update to v.1.2.6 first. Start Formuler remote app and install RCU Firmware update to v. 0.5.3d.
Do first like in 1.
Logic of use, incidently touch would that way change the function and user would not notice. Using in dark, older people etc. many reasons.
Check and pair again BT.
Thank you very much for your aswers
1) Great - I have now updated the app and the remote.
2) Google assistant works now
3) By using that logic, every button should require a 3 sec hold. But I am sure this is not a button that gets accidentally pushed, and even if it should happen - we are spending a lot more time long pressing the button. Have experience from many other remotes with the same button, never required to long hold and it is never a problem.
4) I still do not get a white flashing light... only red and orange. I have unpaired and paired 5 times, always with the same result. Should I not use the BT remote as IR remote when I accept the pairing?
I have a new Formuler Z10ProMax with BT Universal remote, and I have a few issues
1) I am not able to update the remote. My Formuler remote app does not show an update option.
2) Google assistant does not hear my voice after I press the assistant button
3) I really dislike that I have to hold the TV/STB button to change function. Why do we need to hold the button? A simple touch should be enough.
4) When I switch between TV and STB, I do not get any white flashing light. It switches between red and orange. But the light is white when I press any buttons.
I paired the Bt1 remote to my TV using setup ir controls and now my remote won't go back into Bluetooth mode when I hold the tv/stb button it changes to orange or red only not white
Mine also only changes between orange and red, but everything works fine except for I am not sure about how to talk to the Google assistant... I try pressing the google button, but seems like the remote does not hear me.
Even though the light is orange, the Formuler box says the remote is paired, and it works even though the box is on the other side of the wall. So I would guess I am ok? But why does the Google assistant not hear me?
Also a strong supporter of adding EPG search to MYTVOnline2! Amazed this has not been a more strongly requested feature and it hardly has any mentions here on the forum.
Likely an issue with your login. It all works perfectly fine for me and others I’ve helped setup…
Recheck login details or…. Simply create a new one. No harm done
100% sure I am using the right credentials (User ID and Password). If I try to create a new account via MYTVOnline2 I get the same error message as when I try to log on. Also tried to make a new account on the web - same result when I try to connect.
I have the same problem:
”Error while signing in. (-1)
Check username and password or try again later.”
...still - I have an active user on opensubtitles.org
A new Formuler Z10 Pro Max.
