Hi jennylstafford,
The following steps address what you're describing specifically, and should provide a solution:
"Use a verification code on a website or in an app
- Sign in to the website or app.
- If prompted, select the option to use an authenticator app.
- When asked for a verification code, tap the suggestion that appears above the keyboard.
- If no suggestion appears, go to Settings
> Passwords, select your account for the website or app, tap the verification code, then tap Copy Verification Code. Return to the website or app, then paste the verification code into the field."
You can find these steps along with other information that may be helpful, here: Automatically fill in one-time verification codes on iPhone – Apple Support
If you have followed the steps correctly and you still have the issue, let us know if you get any specific alerts or error messages when trying, as those may help us determine what might be causing the issue.
We also recommend restarting your device and keeping it updated as those steps assure you have cleared out any minor software issues and are running the most current version.
Restart your iPhone - Apple Support
Update your iPhone or iPad - Apple Support
If you still have questions, reach out to Apple Support directly, as this may require closer guidance: Get Support
Cheers!