First off, you're definitely on the right track by checking the field-level security and object permissions. That’s often where issues like this originate, but since you’ve already ensured the Guest User profile has proper access, it points to something deeper—probably within AddressTools itself or the way it interacts with Guest User profiles in LWR sites.

Here’s what I’d suggest digging into next:

1. Check AddressTools License Settings AddressTools often has profile-based licensing. Ensure the Guest User profile is included in the AddressTools license configuration. You might need to grant explicit access to the Guest User profile in AddressTools' settings.

2. Guest User Record-Level Access Even though the field-level permissions are set, the Guest User might be failing validation due to a record-level access issue. For example:

Verify that the Guest User has the correct sharing rules or permissions for the Contact object. Ensure that any custom validation rules or triggers related to AddressTools don’t inadvertently restrict Guest Users. 3. Country Picklist Validation AddressTools often relies on standardized country picklists. If the Mailing Country field is a text field rather than a picklist for the Guest User, AddressTools might not recognize the input. Double-check:

The field type consistency (picklist vs. text). That the Guest User can "see" the picklist values if you're using them. 4. AddressTools Integration Settings AddressTools might have some validation configurations tied to specific users or profiles. Head to the AddressTools configuration:

Look for settings related to "Validation on Save" or "Restricted Access." Ensure Guest Users aren’t excluded from certain validation processes. 5. Debugging Tips Turn on Debug Logs for the Guest User. While it’s a bit of a hassle, it can be incredibly revealing. Look for entries from AddressTools when the Guest User tries to save a record—it might highlight exactly why the country validation is failing.

6. LWR Experience Site Settings Since you’re on an LWR site, certain permissions and functionalities for Guest Users behave differently compared to standard sites. Check:

Site Access Settings: Ensure that the Guest User can access any required Apex classes or custom settings used by AddressTools. Content Delivery Network (CDN): Sometimes, LWR sites cache or restrict access to static resources needed by third-party tools like AddressTools. 7. As a Quick Test Try temporarily disabling AddressTools validation for Guest Users to confirm whether the tool is the culprit. If the error vanishes, it’s definitely an AddressTools configuration issue. If it persists, it might be a deeper Salesforce permission problem.

8. Reach Out to AddressTools Support If all else fails, AddressTools has a solid support team. Provide them with the exact steps and error messages—they’re often able to spot issues specific to their product and guide you toward a fix.

TL;DR: The issue likely lies in AddressTools’ profile-based permissions or validation settings, especially around the Guest User profile. Focus on checking AddressTools’ licensing, picklist visibility, and LWR site quirks. Debug logs and support might be your best friends here.