If your Domain Authority has not changed, there could be several reasons for this:

Lack of New Backlinks:

Domain Authority heavily relies on the quality and quantity of backlinks to a domain. If your website hasn't gained new high-quality backlinks or has lost some, it may result in a stable or unchanged Domain Authority.
Fluctuations are Normal:

Domain Authority is not a static metric and can experience fluctuations. It's common for it to stay the same or change slightly over short periods. Moz updates their index regularly, but not on a daily basis.
Competitive Landscape:

If your competitors are also actively gaining backlinks, it may be challenging to see a significant increase in your Domain Authority unless you are actively working on improving your link profile.
Algorithm Updates:

Moz may update its algorithms or metrics, which can impact how Domain Authority is calculated. It's essential to stay informed about any changes Moz makes to its methodology.
Link Quality:

The quality of backlinks matters more than quantity. If your site is acquiring low-quality or spammy backlinks, it might not positively influence your Domain Authority.
Historical Backlink Profile:

Moz considers the historical backlink profile of a domain. If you had a spike in backlinks in the past, the effects might still be influencing your current Domain Authority.
Redirects or Changes in Website Structure:

If there have been significant changes to your website structure, domain redirects, or changes in domain, it can impact how Moz calculates Domain Authority.
Patience is Key:

Improving Domain Authority is a gradual process. It takes time and consistent efforts to build a strong and credible link profile.