TypeError: Cannot read properties of undefined (reading 'REACT_APP_SC_ATTR')

I have a react project I'm trying to get to work with next js

I'm getting the error:

Unhandled Runtime Error
TypeError: Cannot read properties of undefined (reading 'REACT_APP_SC_ATTR')

Error relates to code:

    <StyledEngineProvider injectFirst>
      <MuiThemeProvider theme={createTheme(theme)}>
        <ThemeProvider theme={createTheme(theme)}>
          <AuthProvider>{Component}</AuthProvider>
        </ThemeProvider>
      </MuiThemeProvider>
    </StyledEngineProvider>

If I remove this code the error goes away.