In-Active domains are not charged and refer to domains that have no or defensive SPF/MX records published, where the syntax of defensive DNS records is:
Defensive SPF record
Value: v=spf1 -all
Defensive MX records
Your in-active domains MUST NOT use any of the following features: Hosted MTA-STS, Hosted TLS-RPT, Hosted BIMI, or PowerSPF to be considered as in-active domains.