If the screen below appears after adding your digital ticket, simply close the page and open your Google Wallet, your ticket should now be visible there.
In the Google Wallet app, you may need to switch to the email account associated with your Arsenal membership.
If the email address linked to your arsenal membership is not showing as an option to switch then you may need to create a google account with the email address or you may already have a google account linked to that email.
How do I know if I have a google account with my Arsenal email address?
If you try to sign in using the email address associated with your membership and see the message 'Couldn't find your Google Account,' you'll need to create a Google account using that email. 
When creating the account please ensure you choose the option 'use your existing email' and then you will enter the email address that is on your Arsenal membership account.
If signing in with the email address on your membership account takes you to a password prompt and you don't receive the message 'Couldn't find your Google Account', this confirms that you already have a Google account associated with that email and you can login using the password for that account or you can reset the password.