An ads account being locked out of ads.twitter.com is usually because of the account not adhering to Twitter’s Ads Policy.
Violations of this policy could be related to the account itself (not having an appropriate profile or profile image) or the content of the account such as its Tweets.
Please see the following guidelines about eligibility:
If your account was suspended or locked please first visit the following page and see if it was locked for security reasons:
If you wish to appeal the suspension the following form can be used to appeal: