I am receiving "error 1035" on my iPhone 8 Plus

Visual VoiceMail error that may mean it needs to be set up again. You might also want to turn Live Voicemail off/on to see if it resolves the error. More information is here about setting it up and with some carriers you can go to the Phone app to press and hold the 1 key on the Keypad to resolve the error. Your carrier may not support all of the Voicemail options.

Set up your voicemail on iPhone - Apple Support

That is most commonly associated with a voicemail issue. Contact your carrier for help with voicemail as that is a service they provide.