There was an audience burnout.

Usually, the audience is enough for 2 to 3 months of targeting. Then it needs to be updated. You get bored with your ads and users stop responding, in such cases, you need to update the audience.

Stop ineffective ads and rebuild your audience by expanding interests, but excluding old audiences from the new one so as not to show them to those who have already seen your ads.

Narrow offer, or audience

Perhaps a very narrow audience has been chosen. An audience that is small and lacking. What to do. Expand your audience to reach a large number of users, build relationships and work with a wider audience, creating demand for your services.

Ad burnout

You have found a working connection (ad/audience) and use it only.
Sooner or later, your ad will stop working.
Ads, like the audience, need to be changed.

Constantly test something new. Photos, videos, slideshows, carousel, different offers, etc. You should always be on the lookout for new things and not get hung up on working ads. If they work, increase your budget, but don't stop testing.

Different placements and goals.

If you've set up ads on Stories, try the feed and vice versa.
Try different goals and measure the effectiveness.

The most effective goals for a business account include Traffic, Reach, Conversions, and Engagement. But these goals are not always suitable, it all depends on the objectives of your advertising.
Be sure to use several goals, sometimes it's hard to predict which one will work best.