MyTarget has a limit on the number of ads created.

For new accounts — no more than 30 ads.
For existing accounts, the limit depends on the balance and the number of debits for 3 months: if your balance is more than 3000 rubles or if you spent more than 3,000 rubles in the last three months, for every 150 rubles spent, 1 available banner is added.

In other words, if you have 4500 rubles on your account, you can create 30 ads; if you have 6000 rubles on your account, you can create 40ads.
If you spent 5000 rubles over the past 90 days, your limit is 33 ads.

If you have reached the ad limit, delete unused ads or add funds to your account.