Hi there Thachthao,
From what we can tell, your husband is unable to accept your invitation to join Family Sharing because the invitation is expired. We're glad you've connected with us in Apple Support Communities, and we can provide some guidance.
"Accept or decline an invitation to join a family directly from your device. You'll get an invitation sent to you by email or in a text message. Then you can respond right from the invitation. If you miss the email or text invitation, no problem. You can respond from your device Settings or System Preferences." Learn more here:
Set up Family Sharing
With that said, your husband can follow the steps in the 'Join a family group' section of the link above to join Family Sharing.
We hope this information is helpful. Don’t hesitate to follow up with us here if you have any more questions.
Cheers.