Airtags can't be shared from iPhone 8

Dear Airtag Experts,

Thank you for reading this question. I'm not sure why, but my Dad's AirTags are connected to his iPhone 8. However, when he tries to share his AirTags with my iPhone 12 Mini using the "Add Person" feature with my phone number, I never receive his share notification.

Similarly, when I try to share my AirTags connected to my iPhone 12 Mini with my Dad's iPhone using the "Add Person" feature with his phone number, he never receives a sharing notification.

Could it be possible that the iPhone 8 doesn't support the AirTag sharing function?

Kind regards,

Kevin