Atlassian certifications have an inactive and expiration date.
Expiration is self-explanatory - once this date has passed the only way to get the certification back it is re-sit the exam.
Certifications can be extended at any time by completing a relevant skills badge.
So what does it mean when a certification is inactive? Am I no longer certified but have a grace period to extend the certification for the period between the inactive and expiration date?
from my experience with my certifications so far this inactive status is relevant for solution partners and their requirements to uphold the partner status. I noticed that inactive certifications won't count towards the accreditation.
You are correct, the 3 months between the suspension date and the final expiration date is a grace period during which you can still renew your certification and make it active again with a badge.
For anyone verifying your Certification, the verification window will show 'Expired' during the inactive grace period.
During the inactive period, when you earn a badge your certification automatically renews, and 18 months will be added to its active period starting from the suspension date.