Flutter gsheets read, write and google sign in

I have an android app that uses google sign in to log in and then reads and writes data to 2 google spreadsheets. I have a problem with the google sign in, because when I go back after signing in, I can't log in back again. The other problem I have is in the readpart, since the gscript is returning null, even though there is data in the spreadsheet.
Can someone please help me fix this issue?
Thanks in advance.